* An explanation of documentation structure.
* Added HBP/Ebrains to acknowledgements.

* Modify `cell kind` concept docs.
* Add `cell description` concept docs.
* Reorder the docs so that the recipe, cell kind and description, interconnectivity, hardware management, domain decomposition, and simulation are consecutive. Then start the more detailed cable cell docs. 

`pow(double x, int y)` is implemented as of ROCm-3.9 (May have been fixed earlier, don't have access to earlier versions)

* Add a readme for the C++ examples
* Improved readme for dryrun

Fixes #868, #1107.

Major changes in Python library and documentation:

* Add global state (immutable after initialization) for the Python module that
  manages the mapping between probe metadata types and the method by which the
  corresponding [sample data can be collected and presented as Python objects.
  This is necessary for decoupling the implementation of the simulation wrapper
  from that of the various cable cell probe types.

* Wrap each of the C++ cable cell probe types with a Python function that
  returns a `probe_info` object.

* Add code for converting and accumulating C++ probe metadata and sample
  data, registered in the module global state against the metadata type info.

* Make the `arbor.simulator` object responsible for recording all spike and
  sample data, with corresponding new methods.

* Use NumPy arrays and structured datatypes for returning spike and
  sample data.

* Place Python schedule proxies under an abstract interface so that consumers
  of the proxies can be made generic over schedule types.

* Add unit tests for the `arbor.simulator` class and its new functionality,
  including distributed spike collection.

* Rework all Python API documentation concerning probes, sampling, and spike
  recording; add information on newly exposed cable cell probe addresses.

* Add new python example `single_cell_recipe.py` which is a generic recipe
  version of `single_cell_model.py`.

* Adjust other code in the wrapper and examples to accommodate these changes.

Minor changes in Python library:

* Add equality tests for `arbor.location` and `arbor.cable` Python classes.

* Use the `py::` namespace shorthand more often in the Python wrapping sources.

* Add an implicit conversion for a pair of numbers to `arbor.cell_member`, so
  that e.g. probe ids can be specified simply as `(gid, index)`.

* Add an implicit conversion from a tuple to `arbor.mpoint` so that a
  morphological point can be specified simply as `(x, y, z, radius)`.

* Modify the interface to `arbor.regular_schedule` so that the overloads
  correspond more closely to the C++ API. In particular,
  `arbor.regular_schedule(dt)` now describes a schedule with times 0, dt, 2*dt,
  etc.

Minor changes in C++ library:

* Change test in FVM lowered cell implementation and exception message for
  `bad_source_description`: assert number of detectors is exactly the number
  of sources promised by the recipe.

* Add comment describing `probe_metadata` object in `sampling.hpp` which
  asserts that the type and value of probe-specific metadata completely
  determines the correct interpretation of sampled data provided to a callback.

* Return `arb::morphology` from `load_swc_xxx` methods for consistency with the NeuroML interface. 
* Fix unit tests.
* Fix documentation

Fixes #1230

Fixes #1236

* Add an example describing the content of a recipe in the recipe concepts page in the docs.
* Mention that recipes are necessary, but can be abstracted away using the python `single_cell_model` (Hasn't been documented yet).

Speed up plotting in seaborn.relplot by disabling calculation of confidence intervals

Update the documentation to mention additional packages used in some python examples.

* Various DOC changes/updates, most importantly to:
* Single Cell Model
* Recipe

* Remove blank line from `ball_and_stick.swc` 
* Mention that blank lines in SWC files indicate end of data.
* Check for trailing data after parsing in the python interface.
* Leave stream in good state if `parse_swc` encounters an empty line indicating end of data.

* Rename `as_segment_tree` to `load_swc_arbor`.
* Remove `swc_mode`: `sort_and_validate_swc` now performs the `relaxed` checks by default, `load_swc_arbor` performs the `strict` checks. 
* Change `load_swc_xxx` to only accept `swc_data` as an argument
* Remove default constructor for `swc_data` and enforce validation of SWC records via `sort_and_validate_swc` at construction.
* Add fixes for docs and unit tests.

* Add interface for querying names.

* Add derived mechanisms to list, clean-up.

* Add unit tests.

* Add python bindings and docs.

* Fix some broken links and typos.
* Fix out-of-date documentation.
* Reword some of the existing sections.

Remove Python API ref page, Spack Install, fix some links

Remove imported dependencies in the documentation generation.

* Synced pages between Concepts, Python API and C++ API wherever possible
    * Recipe pages conform between the three section (concepts, python, c++)
    * Cell, Cable Cell and Cell * pages are rearranged and provided with some copy explaining the relationship between them.
* Moved Python API out of Concepts
* Renamed Concepts "How does Arbor work?"
* Added Python Module Index plus mock import of Arbor for RTD build (unfortunately won't show there)
* Broke out Interconnectivity (synapses) page.
* Reworked Single Cell Model page into a quick start, with lots of cross referencing.
* Tweaked logo.
* Added Spack to install options.
* Updated blurb.
* Documentation now follows EU capitalization rules.
* Assorted typofixes

* Add CMake infrastructure for new `arbornml` library comprising Arbor's NeuroML2 (C++) support.
* Implement NeuroML2 parsing and interpretation, using libxml2 for XML parsing.
* Add associated documentation, unit tests.
* Replace `arb::util::optional` with `std::optional` in stitch morphology interface.
* Add optional prefix to `arb::label_dict` import.
* Update CI to test arbornml, with associated workarounds for OS X targets.
* Remove glob functionality from `sup`, as it is no longer needed (it was used for lmorpho) and it triggers yet another OS X issue.

Fixes #1088.

* Move label and s-expr parsing code and unit tests from Python to arbor C++ library.
* Update `locset` and `region` constructors that take string arguments to parse strings as s-expressions or "quoted" labels.
* Modify the input stream modifier used to parse asc files to use a lookup table for substitutions, renamed it transmogrifier.                                                             
* Replace `hopefully` type implemented in python headers with an `arb::util::expected`.
* Add `ARBDEV_COLOR` CMake option that forces gcc and clang to always output color output.
* Allow arbitrary strings in labels in region and locset expressions.
* Add `parse_region_expression` and `parse_locset_expression` functions alongside the existing `parse_label_expression` function for use when a region or locset is expected. These calls will promote a quoted string `"label"` to `(region "label")` or 
 `(locset "label")` respectively.
* Add user-defined string literals for labels so that the C++ interface can use `"soma"_lab` instead of awkward escaping `"\"soma\""`.
* Simplify Python wrapper code.

* Replace usages of `util::any` with `std::any`.
* Modify `util::any_cast` so that it forwards `std::any` arguments to `std::any_cast`; move into own header.
* Prevent `std::unique_any` from implicitly encapsulating `std::any` objects.
* Replace `test_any.cpp` unit tests with `test_any_cast.cpp` unit tests.
* Replace some usages of `std::is_same<X, Y>::value` with `std::is_same_v<X, Y>` as part of general C++17ification.
* Remove `util/variant.hpp`, `test_variant.cpp`.
* Replace occurrences of `util::variant` with `std::variant`.
* Replace `util::variant::get<N>` with `std::get<N>`.
* Replace `util::get_if<N>` with `std::get_if<N>`, passing a pointer to variant instead of a ref or value.
* Add some standard #includes where they were required in the source, but only included transitively.
* Some minor comment tidying and fix-ups.
* Update C++ API docs.

Fixes #1144.

Fixes #1149.

* Update CMake CXX version.
* Make CUDA 10 a minimum requirement and remove CUDA 9 support code.
* Set up g++ Travis tests to use g++ 8.
* Explicitly set C++14 version for nvcc.
* Properly split cuda compilation, including in unit tests.
* Remove unnecessary modcc `SOLVE` warning.
* Update pybind11 module to tag v2.5.0
* Replace `util::size` and `util::data` with `std::` equivalents.

Update flat_cell_builder docs and add deprecation warning.

Addresses #1129.

This PR adds a bunch of high-level docs for concepts related to single cell models.
  * morphologies
  * labels (region and locset expressions)
  * mechanisms
  * cable cells

It adds some python scripts to the `doc` path, which are called during documentation building to generate images of cell morphologies, regions and locsets that are generated in a separate script that uses the Arbor Python API.

The docs are not complete: the cable cell and mechanism docs are unfinished, and the tutorial section needs to build on these concepts to give more detailed step by step examples.

New PR post master rollback; squashed and rebased, but reprises #1111.

* Add (forward) ordered forest implementation, tests.
* Add `segment` region expression; to ease implementation, `msegment` now also knows its own id.
* Add `stitch_builder` and `stitched_morphology`. A stitch corresponds to a labelled, linearly-interpolated segment which can be attached at any point along a parent stitch. A `stitched_morphology` takes a `stitch_builder` object and constructs a segment tree and morphology, and provides a dictionary of stitch labels to segment indices and region expressions.
* Add `import` method for `label_dict`, so that the label dictionary returned by `stitched_morphology` can be merged with an existing dictionary.
* Add section on stitch builder etc. to cable cell docs.
* Update cable cell docs to remove out of date info and to provide some context.
* Describe ordered forest datastructure and interface in a long comment at the beginning of the header file.

Update the docs landing page and add pip install from git.

Fixes #1118

Guide Python users to the Python installation steps early in the installation guide.

* Move `cv_policy` classes to new source files.
* Remove `cv_policy_flag::single_root_cv`.
* Allow all supplied `cv_policy` makers to be restricted a domain specified by a region: the policy is then applied per component, with the boundary points of the completion of the components included.
* Expose `cv_policy` domain in public interface.
* Add `components` function for splitting an extent into disconnected components. Add comment describing what is meant by connected in this context.
* Rename `super` region function to `complete`.
* Add region expression functions `complement` and `difference`.
* Add new locset expression function `boundary` which returns the extrmal points of each component of a region.
* Add new locset expression `cboundary` which returns the extremal points of the completion of each component of the region, which is what we need to close off CVs generated by region-restricted CV policies.
* Add locset expression `support` which returns the multiset support of the points in a locset, i.e. all points in the locset but with multiplicity one.
* Replace hodgepodge of `join` expressions in `cv_policy` implementations with locset `support` and `sum`.
* Inline `mcable::prox_loc` and `mcable::dist_loc`.
* Add cv policy combinators +_and |.
* Add `util::foldl` which acts like `std::accumulate` for ranges, except it explicitly allows mutation of the sequence, and pass the accumulation value by rvalue.
* Add unit tests for mextent components, new locset expressions.
* Remove spherical soma cases from `cv_policy` testing.
* Extent `cv_policy` unit tests to cover new functionality.
* Rejig `cv_policy` unit tests to use the morphology testing predicates.
* Add `cv_policy` documentation to cable cell docs.

Fixes #1058.

* Make recipe return probes as a vector.
* Remove `probe_id` from `probe_info`.
* Rename `fvm_probe_info` to `fvm_probe_data` (everything was being called info, and it was getting confusing).
* Make `probe_association_map` specific to `mc_cell_group`/`fvm_lowered_cell`.
* Change probe_association_map representation: unordered map for probe_id -> tag; unordered multimap for probe_id -> fvm_probe_data. This allows multiple probes to be associated with the same probe id.
* Call sampler callback separately for each probe with the same probe_id.
* Replace location-based probes with locset equivalents.
* Add index for probes sharing a probe id.
* Bundle all probe metadata (id, tag, index, probe-specific meta) into `probe_metadata` struct for passing to sampler callbacks.
* Change simple_sampler to work on `trace_vector`, a vector of `trace_data`. The _i_th element is the data from probe with index i.
* Consolidate hash composition and `std::hash` specialization code in new...

Fixes #1037. 

* Add fake unmatchable spike events to event queue for each exact sample request, so that integration boundaries align with exact sample times.
* Update probe-demo for exact sampling.
* Add copy assignment for `cable_cell`.
* Extend max args for ARB_PP_FOREACH to 20.
* Add unit test for ARB_PP_FOREACH.
* Use ARB_PP_FOREACH to instantiate backend-specific probe unit tests. This also fixes the GPU probe tests that were using multicore backend.
* Add unit test that exercises exact sampling requests combined with regular events in a gap junction context.

Fixes #589 and #730, providing cell-wide probes and a correct total trans-membrane current.
Fixes #822, providing spatial interpolation of membrane voltages as governed by cable resistivity and diameter.

* Add partition of point mechanism target vector by cell index to `fvm_mechanism_config`.
* Fix sign error in axial current interpolation.
* Replace `fvm_probe_info` with class that wraps a variant type capturing one of a set of backend-cellgroup probe translation representations: `fvm_probe_scalar`, `fvm_probe_interpolated`, `fvm_probe_multi`, `fvm_probe_weighted_multi`, `fvm_probe_membrance_currents`.
* Refactor `fvm_lowered_cell_impl::resolve_probe_address` so that it avoids the long chain of if-else tests on wrapped `any` type with an invocation of `util::any_visitor`. Each specific cable cell probe address representation is translated into one of the intermediate `fvm_probe_info` variants via an overload of `resolve_probe`.
* Add new non-scalar cell pr...