Add IGWN Sphinx Material theme

Note: This is related to !117 (closed).

This MR adds a Material Sphinx theme so that it looks similar to Mkdocs. It's made to look like this site.

It's not pixel perfect, the most obvious difference is the margins which are smaller in Mkdocs.

Tell me if this looks ok, or if not I can make more mod's. I think it looks somewhat decent.