Provide (experimental) support for mkdocs documentation

[jaimergp]

Description

This is an attempt at using mkdocs + material + mkdocstrings work as a replacement for ReadTheDocs.

URL: http://openkinome.github.io/kinoml/

Tasklist

• [x] Remove mkdocs branch from Docs CI events

Gotchas

• There's no standard autodoc replacement; instead there are many which cannot be considered very mature yet. One striking difference might be that since mkdocs is markdown based, docstrings purposedly avoid using numpydoc docstrings because they resemble RST too much. I don't see this as a problem for new projects, but might be something to discuss. There are other plugins in the making that will add support for numpydoc but none robust yet.
• We won't deploy to readthedocs but to github.io automatically, thanks to GH Actions.
• It looks too beautiful!

[jaimergp]

I just discovered all the Material theme extensions (which I promptly enabled) and I am deeply in love.