Changes a bunch of :doc:`/cmd/*` to :cmd:ref:`*` with the intention of changing it later to something that replicates the previous effect of displaying the commands `short_help`.
Removes group parsing from command ref domain, instead relying on a 'groups' object in the cmds.json file.
`docs/source/cmd` is no longer ignored or cleaned.
Add `doc_string` field to `Pass` constructor
Add `docs/util/newcmdref.py` to contain command domain
Update `docs/util/cmdref.py` with `cmd:usage` and `cmd:optiongroup` for describing commands.
Functional, but WIP.
Properties are both an option:
```
.. cell:def:: $add
:properties: is_evaluable
```
and a field:
```
.. cell:def:: $eqx
:property x-aware:
:property is_evaluable:
```
Properties as an option appear in the property index: linking a given property to all cells with that property; while properties as a field display with the cell.
Remove `/source/cell` from .gitignore.
Add a few initial cell pages.
Add YosysCellGroup documenter and cell:group directive.
Update Documenters to use nested json.
Better nested tocs for group.module.source layout.
Fix RTD not including source with warning
`WARNING: invalid signature for autocellsource ('/home/docs/checkouts/readthedocs.org/user_builds/yosys/checkouts/manual-rewrite/source/generated/simlib.v:$alu::__source')`.
