Errors are not public

[samueltardieu]

The try_new() method of VirtAddr and PhysAddr may return respectively VirtAddrNotValid and PhysAddrNotValid. Unfortunately, those error structs are defined in the private module addr and are not reexported, so their content cannot be accessed and they can't be stored in other errors.

It would be great to export both of them.

[phil-opp]

Thanks a lot for reporting! I would be happy to merge a PR that reexports these error types too.