Here's my proposal for a new website for mesa3d.org, minus most of the
content. This consists of a front-page and a news-archive, and not much
more. The rest of the content will be linked to docs.mesa3d.org, which
will contain the technical documentation.

This separation between techincal documentation and a "marketing"
website, allows us to use the best tools for each purpose:
- Sphix is great at creating techical documentation, but lacks features
  like pagination for news archives, and is not very flexible in how
  much can be specialized.
- Hugo is great for building websites, but can't easily generate other
  documentation formats, and it's tree-structure isn't as nice for
  in-tree documentation.

There's only the front-page (and the 404-page) for now. In particular,
here's what's missing as of this commit:
1. The news will be converted from the main repo by some scripts in a
   later commmit.
2. Similarly, link-compatibility redirects will be converted from the
   main repo ...