Adds an IA which plays at the 2048 

Hi everybody, this is my first pull request :)
I've added an IA which works very well in my humble opinion.

I'm running the benchmark (for the latest version) in this very moment so I can't give you the right but it seems to me that it have very good performace (Average score > 30k).

I'm not a Python guy, thus the code/style can be improved: any suggestion will be greatly appreciated! :)