Add compatibility to Ruby 2.0+ with Rails 4.1 and 4.2
- Remove machinist, make model generation more robust and simplier
- Use polyamorous master because it just compated with Rails master
- Brand new Context class, because JoinAssociation changed a lot
- Add 4.1 and 4.2 folders under adapters
- Add some ! methods to visitors, so that we can throw some unexpected behaviors from them
- Split specs into 3.x-4.0, 4.1, 4.2 folders in order to make tests easier
- Make all specs green from Rails 3.0
- Pend some specs because of unnecessary behaviors on Rails 4.1 & 4.2 I think