Get rid of re-implementation of sortBy

I have no idea what this was doing lying around here, and due to the
usage of tuples it's actually slower, too.

Signed-off-by: Mateusz Kowalczyk <fuuzetsu@fuuzetsu.co.uk>
Only warn about missing docs when docs are missing

This fixes the ‘Missing documentation for…’ message for modules with
100% coverage.
Add test case for inter-module type/data family instances

These should show up in every place where the class is visible, and
indeed they do right now.