Port DumbledORM ResultSet

I came across a comment from you that you were interested in porting the ResultSet class from DubmledORM to Paris. I really liked DombledORM's approach so I started using it in my project as well. This change adds the ResultSet to Paris, allowing for some fancy jQuery-like syntax. Example:

    Model::factory('Widgets')->filter('expired')->find_many()->delete();

I ported it to Paris, which seemed like the most logical choice to me at the time. If you prefer, I could also try to implement it on Idiorm itself, which would fix your j4mie/idiorm#22