Add utility for retrieving full import paths

[makspll]

As discussed in here: rust-lang/rust#104651 (comment)

It would be useful to provide a utility function to retrieve import paths for items.

[Enselic]

Hmm how did you end up in this abandoned git repo? Did I forget to update some link somewhere?

In any case, there was a misunderstanding, see rust-lang/rust#104651 (comment) 🙂

[makspll]

haha, I have no idea, must have been tired