The `label_dict` Python wrapper caches label strings and their descriptions in order to
provide a convenient Python iterator interface and `[]` access. These were not being
properly updated or set when the label_dict was constructed from a C++ label_dict.

* Update URLs to arbor-sim.org
* update badge links

Add a CI test for ARM-SVE

- compiles and runs the unit tests with vectorization enabled for the `armv8.2-a+sv` architecture
- uses a dedicated gitlab runner on ault.cscs.ch

Fixes #1498

Fixes issue #1529.

* Adapt CSS for the HTML5 transition in docutils 0.17
* Fix some reST markup errors
* Add meta-tag to enable indexation control at Google (current indexation appears at least a year old).

Fix mistakes reported by @Helveg in the Python tutorial docs. 

* Add a GH workflow to build and run Arbor tests and examples with Clang sanitizers.
* Fix some uninitialized struct members; missing `override` qualifiers.

* Use a struct with meaningful field names instead of a `std::pair` to represent elements in `pw_elements`.
* Describe explicitly the semantics of the zip operation.
* Update implementation and add unit tests to suit.
* Add comment explaining `pw_elements::equal_range`.
* Remove parameter names from unused parameters in `impl::piecewise_pairify`.

* Correct bounds check order in communicator.
* Use `.at()` in test recipe to catch failures in bound checking.

* Exit with correct exit code from Python test runners.
* Fix unit tests that were using older APIs.

* Remove std::filesystem to workaround OSX features; use `std::string` in interfaces expecting a path.

Set option `-mcpu=aarch64` for target `aarch64-apple-darwin`

In response to:

https://gizmodo.com/u-s-federal-investigators-are-reportedly-looking-into-1846707144

Rationale:
* CodeCov didn't detect the breach for two months
* They took a further 2 weeks to alert users after that
* Their efforts to address the issue after that have been painful to watch
  * https://github.com/codecov/codecov-action/issues/281#issuecomment-823407167

* fix mech_vec
* fix fvm_discretize
* small fixes

* Fixes incorrect `current-clamp` generated s-expression. 
* Adds unit test.

Fixes #1486

* Move `assign` out of the `detail` namespace in the SVE SIMD implementation code.

* Add Zenodo citation snippet.
* Correct Nora's last name, which is Abi Akar.
* Small css fix for change in docutils, see: https://github.com/readthedocs/sphinx_rtd_theme/issues/1115

Fixes #1297.

* `i_clamp` constructors take new optional phase argument.
* Pulse or box envelope clamps are now provided by the static method `i_clamp::box`, taking onset, duration, and amplitude parameters.
* Bump pybind11 version so we can have keyword-only arguments in the Python API.
* Make frequency and phase keyword-only arguments to Python `iclamp`.
* Change frequency units for clamps from Hz to kHz for consistency with other interfaces.

Fixes #1454.

* update and simplify the `load_swc_neuron` reader to match the simplified and more correct interpretation in NEURON 8
* update the documentation on the interpretation, and add details about how it still differs from the neuromorpho descriptions. 
* update unit tests to reflect new interpretation
* add a unit test that reproduces a complex case from the NEURON test suite.
* remove the `load_swc_allen` C++ and Python calls
* add links to NeuroMorpho site in the documention

Fixes #1445.

Always install Python module inside CMAKE_INSTALL_PREFIX, unless the user explicitly sets the ARB_PYTHON_LIB_PATH CMake variable.

Update documentation on installing and building the Python packing using CMake to have a detailed example of how to install the Python module inside a virtual env.

Fixes #1403

* Correct the installation page.
* Custom css is not supported by theme, so a css snippet improving table formatting was moved to the theme css.
* Non cable-cell concept docs were wrong, improved formatting
* Some typos

Co-authored-by: @clinssen 

Replicate the spack `package.py` from the main spack repository into the arbor repo.

Some small updates were made:
- Correctly provide a url for the GitHub tagged release
- Specify minimum pybind11 version 2.6

Fixes #1465 

* Install gcc-8 and clang-8 in GitHub Actions Ubuntu image, as these had been removed in an update 29.03.2021. See https://github.com/actions/virtual-environments/issues/2950

* Implements parsers and writers in `arborio` for the s-expression based Arbor Cable-Cell Format defined in #1336.
* Moves `s_expr.hpp` to the public interface.
* Adds python wrappers to support the features in pyarb.  
* Adds unit tests.
* Adds docs.

Fixes #1336
Partially addresses #1233

Co-authored-by: C.A.P. Linssen <charl@turingbirds.com>