Fixed up producer structure and broke out Cassandra classes into multiple
files.
Squashed 'avro/' content from commit afb745a

git-subtree-dir: avro
git-subtree-split: afb745a1dcb54865e40bfca9998444b3a968325a
Merge commit 'aa9c10a969fe34fd9c43cbe2c600f9c2470b3746' as 'avro'
Started integrating in Avro schema repo.
Producers' flush() now returns a boolean.
Integrated further with the Avro schema repository by allowing schemas to be
looked up by ID as well as registered with the server.
Working on what will become the Kafka producer.
More work on the kafka producer, added queueing and flushing code.
We now have an Avro serializer that will generically serialize insert
mutations to the InsertMutation Avro schema using maps.
More wiring up of the generic avro serializer and kafka producer.
Made sure we don't get other versions of avro via Astyanax.
Use __ instead of : as a db/table delimiter.
++TODO