Added retry policies for Query and Batch Statements. Policies can be defined at the cluster or per query. Added test cases for retries and added test case for batch statement limits.
Changed TestBatchLimit to test that the correct error is being returned.
Simplified session.executeQuery to use a pointer to Iter instead of creating a new object.
Merge pull request #112 from phillipCouto/retrypolicy

Added retry policies for Query and Batch Statements.