Cassandra compatibility

Astyanax uses a versioning scheme that is internal to Netflix and does not match the Cassandra versioning scheme. The below table provides a mapping from astyanax version to cassandra version.

Astyanax	Cassandra
1.0.4 ... 1.56.22	1.1
1.0.0 ... 1.0.3	1.0.8
... 0.8.11	0.8.6