Automatically generate documentation

Context from https://github.com/SymbiFlow/fasm/pull/28:

> > > Are the docs from the Python code and C++ code getting included into the sphinx output?
> > >
> > @mithro I ran `make html` in `docs/`, but I don't see anything related to the source code.
> Sounds like it was never set up for this repository (hence it might be okay to bump this to a github issue to follow up on). Please reach out to @rw1nkler, he did this for Verilog To Routing - https://docs.verilogtorouting.org/en/latest/api/vpr/contexts/