Generate and publish HTML documentation

For @ksojakova and @jamie.nomadic 's work on the blog post https://gitlab.com/nomadic-labs/private/blog/-/merge_requests/130 on the FA1.2 work (!97 (closed)) it would be convenient to generate and publish a hyperlinked documentation of the coq development.

My research (i.e. asking on #coq-help) has lead to two main proposals: coqdoc + coqdocjs or alectryon . Either way it has to be setup, and the rendered html must be hosted. This should ideally be done in the CI (for all branches?).

One advantage of the coqdoc approach is that some degree of support is already wired into our build system (make html in src/michocoq produces a documentation). However, the documentation is not actually very helpful. It is just a rendering of the source files in HTML, a table of contents with an entry per file and a huge index of identifiers.