Automate the generation of docs/drivers.rst

While investigating #342, a thought struck me:

Would it be possible to automate the generation of `docs/drivers.rst` when generating `circuitpython_library_list.md`

A possible source of information would be the `keywords` passed into `setup()` in `setup.py` on the libraries that are uploaded to PyPI. On boards without a `setup.py`, a `keywords.txt` could be created. This could also possibly be made feature searchable like the boards matrix has recently.

Thoughts?

Start by locating the process that generates circuitpython_library_list.md and inspect how docs/drivers.rst and the boards matrix are currently maintained. Review setup.py metadata for PyPI libraries and consider how keywords.txt would cover boards without setup.py. Done means the driver documentation is generated consistently and supports the proposed feature search.

Written by the indexing model from the issue text.