Slight refactoring
Move Method, Signature to their own files/rename to MethodComparison, MethodSignature

Copy a lot of ArgumentErrorizer's internals into Helper to support MethodSignature
ArgumentErrorizer delegates much of its functionality to Helpers
Add more shit to todo so I don't forget it
Commit half-assed types/names pre-refactoring

Committing just to get the ideas on there, but really I'm going to
refactor the error messages so that they don't look like this. Didn't
want to add tests on them as I was about to change them, but don't have
time to change them tonight.