* Render descriptions as Markdown
Following https://github.com/NixOS/nixpkgs/pull/237557, DocBook
descriptions are not supported any more.
We cannot use options.json any more because it still has DocBook
descriptions in 22.11, so read the options from the modules directly.
* Bump VERSION
* Fix `fix-xrefs.lua`'s empty link detection
Since we now go directly from Markdown to HTML, Pandoc sees actually
empty links instead of `???`.
* Bump VERSION
