* Refactor Documentation layout. 
* Display Spack page.
* Display Extending catalogues page.

Fixes #1353.

* Update `README.md`: moved citation to `doc/index.rst`.
* Advertise Py3.9 compat PyPI in setup.py
* Fix typos.

* Tutorial ring network added. A few typos fixed, crosslinks fixed.
* MPI tutorial added.
* Improved SVG generation, added separate label scaling, increased default label size.
* Bugfix: didnt generate cable region in gen-labels.py used in `concepts/morphology.rst`.
* Termified Interconnectivity page.
* Termified probe nomenclature page. Will be moved in [this PR](https://github.com/arbor-sim/arbor/issues/1353) from python/simulation to concepts/probes_samplers.

`/doc/scripts/divio_docs_theme` has the contents of the tarball from PyPI, slightly modified (custom fonts removed, font-awesome reduced to woff2, logo enabled, divio banner/analytics removed.).

* add neuroML example
* no test, because GH actions arbor is built without neuroML support

- Make reversal potential `e` a global parameter of `pas` to avoid inconsistency 
  (reversal potential is represented by a RANGE parameter, despite it not being a conductance multiplier see #1052)
- Adjust default value of `e` to -70mV (as in Neuron)
- Streamline docs,  which use `passive`, `el`, and `gl` instead of `passive`, `e`, and `g`.

Closes #1052

* Sync Cable Cell page names and ordering between sections (concept, python, cpp). Except cpp cable cell page. Is still one big page.
* Move CV definition across categories to consistent location.
* Move decor to separate page (cpp currently missing decor documentation) because it's a top-level concept that should be in the TOC like the other ingredients of the cable cell.
* Slight rework of Concept intro and Cable Cell pages.
* The Cable Cell page is now basically an intro, and lay out how the other pages/concepts relate to each other.

Reomove Travis CI integration.

* remove Travis yaml and build scripts
* remove Travis badges from README and RTD docs
* replace Travis badge with GitHub Actions badge
* add a RTD badge to the README

Fixes #1338.

* Move contents of `arbornml` to to `arborio` 
* `arborio` will be built with NeuroML2 morphology support if `ARB_CMAKE_NEUROML` is set. 
* Wrap `arborio::neuroml` and `arborio::morphology_data` for pyarb.
* Add documentation.
* add `neuroml` flag to `setup.py`

Fixes #1256
Fixes #1234

* Added a `POST_EVENTS` procedure to nmodl, that takes an argument that represents the time since the last spike on the cell. In the event of multiple detectors on the cell, and multiple spikes on the detectors within the same integration period, all spikes will be processed by the synapse. Spikes are processed only once and then cleared.
* Added 3 vectors to the shared state required to dispatch post-events: `cv_to_cell` map, `time_since_spike` holding max(num_detectors) slots per cell, and `src_to_spike` mapping spike sources (detectors) to slots in `time_since_spike`.
* Renamed `vec_ci_` to `vec_di_` (to better reflect that it stands for **domain index**). Named the new `cv_to_cell` index as `vec_ci_` in the mechanisms.
* Fixed existing unit tests and added new tests for the new post-events functionality.

Fixes #1206

First phase of dynamically loaded mechanism catalogues.

- Add functionality to load and use catalogues from DSOs in Python and C++.
- Add documentation and support scripts to build catalogues DSOs.
- Re-factor CMakeLists.txt for mechanisms
- Limitations
  - Needs (compatible, preferably identical) arbor sources when building catalogues
  - Can only work on MacOS and Linux (uses dlfnc)

* Used Sphinx glossary directive to create terms that can be referred to in `concepts/morphology.rst` and `concepts/labels.rst`.
* Added note box on difference with Neuron, add source for NEURON cylinder discretisation
* Parameters added to svg generation script: turn off colors, root
* Fix cpp TOC duplication, match ordering in other sections.
* State default cv policy
* center/re -> midpoints
* Clarify and remove compartment term

Introduce two minor changes to the Python API
to handle mechanism_catalogues idiomatically.

Instead of

import arbor as A

cat = A.default_catalogue()

if cat.has('hh'):
  print("Found HH.")

for mech in cat.keys():
   print("*", mech)

we can now write

import arbor as A

cat = A.default_catalogue()

if 'hh' in cat:
  print("Found HH.")

for mech in cat:
   print("*", mech)

which is closer to the expectations of Python users.

* Add docs tutorial page for single_cell_recipe.py example
* Adapted single_cell_recipe.py slightly
* Improved labels and fixed some broken cross-linking
* Fixed a typo here and there

Fix some broken hyperlinks in the rst documentation.

* Add the ability to use json and pybind11 libraries installed on the system instead of the
  vesrsions of those libraries bundled as submodules in the Arbor repository
  * Turned on by default
  * Toggled using the new `ARB_USE_BUNDLED_LIBS` CMake flag
* Update documentation for installation
* Update CI and pip workflows to opt in to the bundled libraries

Revert a change introduced in #1282 that required the python module for arbor to build the documentation.

This breaks the readthedocs build, where arbor is not available.

* Remove arbor dependence from `doc/conf.py`, reverting to the original "out of core" approach
* Fix other recently introduced issues that lead to CMake errors when configuring the documentation
  when the Python target is not configured.
  * The CMake variable `PYTHON_EXECUTABLE` wasn't set, but was required to make calls to the
     Python interpreter.
  * Instead of relying on pybind11 to find Python, explicitly detect it using `find_package(Python3 ...)`
  * Make Python3 a hard requirement when building the Python wrapper
  * And a soft requirement otherwise, that will fail only when the docs are built.

Update the PR licensing rules in the PR contribution guide.

* Add 2 new examples to `python/examples` and their corresponding tutorials in the docs. 
    1. `single_cell_detailed.py` : a slightly more complex example using `single_cell_model`
    2. `single_cell_detailed_recipe.py`: equivalent to `single_cell_detailed.py` but using a recipe. 
* Change `load_swc`-> `load_swc_arbor` for consistency.
* Run Sphinx with specified PYTHON_EXECUTABLE.
* Set PYTHONPATH env var in doc/CMakeLists.txt, such that it propagates correctly, including locally.
* Build pyarb BEFORE html such that docs build can import arbor in Github Actions script.

Add API for `single_cell_model` and `label_dict`

* `concepts/cable_cell`: number subcategories to better illustrate document structure.
* `concepts/labels`: concretize -> thingify; more on label dictionaries.
* `concepts/mechanisms`: Some info on modcc, link to nmodl files in repo.
* `concepts/morphology`: NeuroML section and some notes on branches/segments

* Expose and document the (segment id) region expressions.
* gen-labels.py was not up to speed with decor #1235.
* The SWC example is read from disk and inserted into the docs verbatim.
* The same file is used to generate the image.
* The missing decor constructor has been added.
* Generating inputs.py on the fly when building docs. That should prevent this issue from coming up again.

* Docs: emphasised the option of having pip install a local copy of the Arbor source.
* CMake: default Python library install path to `${PYTHON_EXECUTABLE} -c "import sysconfig; print(sysconfig.get_path('platlib'))"`. Fixes #1100.
* CMake: remove ARB_PYTHON_PREFIX option, added ARB_PYTHON_LIB_PATH option. We cannot know in general where in the prefix the packages are expected by Python.

Wrap place_pwlin interface to allow querying rich geometry information from cell morphologies.

* Add Python bindings for the `place_pwlin` and `isometry` classes.
* Add equality test for Python `mpoint`.
* Add unit tests for new Python interfaces.
* Split C++ API morphology documentation into its own file.
* Add C++ API and Python API documentation for `place_pwlin` and `isometry`.

Extend Ptyhon recipe wrapper to support setting of global cell properties.

* Rename `pyrecipe::get_probes` to `py_recipe::probes`
* Remove `global_properties_shim` : It's easy to make mistakes with the class, as it holds a `mechanism_catalogue` and a `cable_cell_global_properties` which holds a pointer to the catalogue. This would likely have caused issues with the users.
* Expose `py_recipe::global_properties`

Make the `cable_cell` interface read only by passing the decorations
to its constructor in a new `decor` type.

C++ library
* Remove the paint/place/set_default interface from `cable_cell`
* Create a `decor` type that:
  * stores lists of paintings and placings
  * stores a set of cable cell parameters
  * uses the `paint`, `place`, `set_default` interface that was deprecated
    from `cable_cell`.
* Create `paintable`, `placeable` and `defaultable` variants that are sum types
  over the respective types that can be painted, placed and defaulted.
* Remove the overloaded `cable_cell::paint`, `cable_cell::place`,
  `cable_cell::set_default` methods to single methods that consume the sum types.

Unit Tests
* Many small changes because many many tests use cable cell API.
* There were no `cable_cell` unit tests! Not such a big deal, since cable_cell
  is tested implicitly in so many other tests
  * but I added cable_cell tests: not much at the moment but will quickly fill
    ...

* Move PR message instructions to 'Making a PR' section.
* Move coding instructions to 'Write code' section.

* Remove mention of the Copyright Transfer Agreement

Update CMake configure to look for svgwrite when building docs.

Fixes #1128.

Set up contribution guides.

Add a contribution guide, as well as 
* Added contribution section.
* Moved content here from the wiki regarding (contribution) processes.

Also added some incomplete / placeholder sections that can be improved later.
* How to write an example
* How to add a test
* Coding style guidelines

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