ocaml
Driver: generate "external" pages
This adds generation of (basic) pages for:
- A "list of all packages" page (at the root of the doc)
- A landing page for each package (in the
<pkgname>/folder) - A landing page for the list of libraries (in the
<pkgname>/lib/folder) - A landing page for each library (in the
<pkgname>/lib/<libname>folder)
This PR does not touch only the driver: I had to add the possibility of an empty --parent-id for the "list of all packages" page.
I also had to avoid "relative references" in the generated pages as they are did not resolve. I used `rooted absolute references instead, and I will investigate the bug.
This will hopefully be useful to test various ideas for the breadcrumbs.
(Hopefully, this can be made less clicky by having the landing page of a package be better (similar to odig's one / ocaml.org's one), but it's nice that library list and library landing page exists to avoid 404 pages eg on handcrafted path)
I think it'd be useful to have some tests for the changed functionality in odoc itself.
