[docgen] Add prefix to module names for generated documentation

[konsumlamm]

Summary

It would be nice if modules had the full path prefix in the heading of their generated documentation. For example, for the standard library, this would mean that all modules (or only the ones in the std directory) would get a std/ prefix:

This should also work for nested paths, for example:

Advantages

• It wouldn't be necessary anymore to add a note that a module needs to be imported with a std/ prefix
• It is encouraged to use the full path prefix (at least for the standard library) anyway, so this would help to push that