[Typer] Type inference paper

To whoever's interested in helping:

I just pushed to the `report/hmdup` branch a (very much) work-in-progress article where I try to document the type inference algorithm of Typer (well, more like the one I'd like to use than the one we do use, so it's a mix of "document" and "cleanup/fix" and "after-the-fact design").

If you're interested in helping, I suggest you try and understand what is currently there and then come back with questions about what you don't understand. You'll also see a boatload of FIXMEs which you're welcome to try and attack.

I think currently one of the more feasible and useful things would be to work on the proofs that our inference for System F is conservative, sound, and complete.

Stefan