Statify and curate the overview of guides

Right now a Jekyll upgrade on GitHub has broken
the page. The first commit tries to alleviate this
by creating a cleaner, static markdown version of
the page.

The subsequent commits reorder and categorize the content.
That's some of an intermittent bug in jekyll. It cuts some of the pages from the toc and from the menu at the right. I hope that I finally fixed that bug in a recently submitted pull request.