Switch mkdocs and readthedocs themes into installable third-party-packages.

[redtide]

I would like to fork the main theme and create a new one similar to material but without custom css.
I tried with mkdocs-bootstrap but it looks quite outdated, so I wonder if it could be possible to have mkdocs and readthedocs themes as modules with their own repo, so people can directly fork them without keeping the entire project to contribute to them.

[tomchristie]

Having both the default and readthedocs themes as installable third-party-packages would be an improvement, yes.

If anyone is interested in taking either/both of these on, that'd be most welcome.