Basic support for rails 4.1

This is a few fixes to get forceps to mostly work with rails 4.1. I don't think its backwards compatible though.

I wasn't able to get has_and_belongs_to_many associations to work because they have completely changed in 4.1. They are now modeled as a has_many to a generated class. I'm excluding that generated class, so if you don't use that relationship, then forceps will work.