Add a few extra tests for tuples
Added datatype_utils file
Minor tuple test adjustments
Merge branch 'tuple-test-merge'
Fix typo in getting started guide

Fixes #154
Docs and example for Cluster.register_user_type
Update API doc methods
Friendlier exception when user type does not exist
Add comments for recently submitted tests
Docs for cassandra.encoder
Document Session.encoders
Don't depend on v3 protocol for reading UDTs