Move from Jekyll to MkDocs

[jgebal]

We should in fact move away from Jekyll documentation generation to MkDocs. It is far more fitted generating documentation and already use it to generate some basic html docs that is the shipped with source code

So we could kill two birds with one stone that way, https://www.mkdocs.org/

[jgebal]

We could use the very much successful https://github.com/squidfunk/mkdocs-material https://squidfunk.github.io/mkdocs-material/