Unlike the XML doc renderer, the AsciiDoc and CommonMark renderers don't
pretty-print certain complex types, like literal expressions, DocBook
literals, and derivations. These types are dumped into the documentation
as JSON.
This commit parses and unwraps these types when loading the
JSON-formatted NixOS options. The AsciiDoc and CommonMark renders have
also been combined into a single script to allow code reuse.
