Fixed up netris!

another day another pull request :P 

I fixed up netris so it work properly and is pretty clean. grid.rb could use a clean up I think maybe. Also I have 2 questions while in the process of redoing this game.

1. Is there a way that I can `define_actor_view` and then use that view for several different actors? if so it would really clean up most of the actors in netris
2. How can I define methods on an actor that can be called by external game logic, either from it's behaviour or from its view.

cheers!