Add documentation arguments to builder

[bayi]

New arguments for documentation generation

This PR adds the following new arguments to builder:

• doc-project= String: The project name that should be displayed in the documentation. Defaults to the soc name.
• doc-author= String: The author of the documentation. Defaults to LiteX
• doc-extra-config= String: the extra config options that should be included in the generated sphinx conf. ( Like setting a different theme )

The argument member property names have underscores instead of dashes in their names.

[enjoy-digital]

Thanks @bayi, this is interesting. Some work has been planned on documentation in September, I'll probably wait to start this to also closely review/merge the PR.

[bayi]

Well the reasoning behind my changes are:

I wanted to use a different theme for the sphinx docs, so installed the rtd theme and i had to actually copy the interconnect/builder.py to my project and just give it the html_theme = 'sphinx_rtd_theme' for the extra config.

Now i can do that with args from my soc definition.

Im using it like this:

Which ends up with a nice documentation generated like this:

Also while we are here, do you know how can i make the CSRField names fit the WaveDrom graph if they are longer ? :)