Show packages and libraries in the breadcrumbs
This is still work in progress as pages that are inside a library are not recognized and the library name might be inconsistent with the one passed to the link command.
This makes the breadcrumbs more readable by removing uninterested components and make the beginning of the module path more recognizable.
The `Library constructor is added to identifiers to propagate this information.
This change requires a change in sherlodoc, likely due to the change in the identifier type.
Do you have a branch with the required modification, so that I can test this PR?
Oops I forgot about that. Here's the fix: https://github.com/jonludlam/sherlodoc/pull/1 (branch odoc3_breadcrumbs_library)
I'll put this PR as a draft while I work a bit more on breadcrumbs to be sure it's the right direction. We'll have to propagate the "short title" of pages into the breadcrumbs, also for package and library index pages, and I don't know if this change will still be required for that.
Closing as this is probably not the right approach. Maybe https://github.com/ocaml/odoc/pull/1196 is better.