docs: Update code base to allow running of Sphinx for generating PyGObject documentation
Submitted by Simon Feltman
The idea is to follow the Python community standard of using Sphinx for internal documentation of the code base. It is unclear if this idea can carry over to into generation of documentation for the typelibs coming from "gi.repository" but it is at least useful for maintainers to have docs for the PyGObject machinery and conformance to some style. Initial commits have been made in an attempt to converge on a single doc style throughout the code base that is Sphinx compatible:
A preliminary style guide has been created here: https://wiki.gnome.org/Projects/PyGObject/StyleGuide
Ideally I think we should use Google style doc strings  in combination with the napoleon extension to Sphinx . But at the moment it seems buggy when run over the codebase due to a lot of the dynamic tricks used in PyGObject.
Next steps would be to work through creating a make rule and committing initial index.rst and related setup files. Possible deletion of the files in "pygobject/docs" as they seem unused. We can then use this location for Sphinx documentation.