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 in a later commit as well.
3. The release archive is missing. We never advertised this under
   mesa3d.org, but rather mesa.freedesktop.org. The fact that these
   sites point to the same one is an implementation-detail.
4. Any custom pages are left out for now. We can iterate on the
   separation between this and the docs site after we've landed the
   initial version, I think.