ocaml-http: extend MDX to lib/http_version.mli
Add http_version.mli to the (mdx ...) stanza. The two examples
were broken: one had OCaml-comment annotations describing the
result, the other was a duplicate inside [val alpn_protocols]
that wasn't valid OCaml. Replaced the module-level example with a
real assert and turned the per-val one into a See-pointer.