duplicate pandu-rao's doc fixes in the readme
Fixed a bug when NetworkTopologyStrategy is used.

Although the Cassandra documentation implies that the
`replication_factor` parameter would be ignored in this case its
presence will cause an error when creating a keyspace using
NetworkTopologyStrategy.
Merge remote-tracking branch 'upstream/master'
Added guards to handle None value in Date and DateTime column to_python conversion
Added guard to handle None value in Date column to_database conversion
Add testcases for guards for None in date, datetime conversion
Fixed bug in test case and expanded test case to include values_list
adding stubbed ttl query tests
adding batch and ttl to docs
adding failing tests for empty container column saving
adding update method to model docs
separating inserts, updates, column deletes and query value logic
ttls are working off the Class and instance
ttl statement fragment
updating update method to only issue set statements for modified rows and counters
fixing container column bug that would write insert empty container columns
adding tests around empty container insert bug fix
added consistency constants to top level
merged blind updates
test that ensures TTL is called on update