boto.DynamoDB2 support

* Numerous changes to support boto.DynamoDB2, and its new method query_2
* Hash keys can now be anything and not just latin, they are packaged through hashlib
* A pop dict-like function
* DynamoDB2 supports save by comparison, so some code can be safely deleted (still haven't fully tested yet)
* __getitem__ in Dynamo object now supports also a tuple, in case you want to specify on the fly the base Table class. This became a need when I wanted to create pro grammatically create DynamoDB tables