I added support for non-standard foreign_keys in has_many relationships

I used your excellent plugin to reverse-engineer a legacy database with over 400 tables. It works great. 

But one small thing was missing: the has_many relationship did not reference the foreign_key name, so I added this to your code via my commit https://github.com/alphabet/rmre/commit/4860c31cf3e401dfc30e1a8983bdeed4fb85b04b.

When the foreign_key name matches the rails convention, it does not add anything to the generated model.