Switches to cql-rb, supports cassandra >= 1.2/cql >= 3.1.0

Some of these changes are unfortunately breaking due to changes in CQL and the cql-rb adapter. I recommend a major or minor version bump.

We'll also want to adjust adapter-cassanity if we want to support per-statement replication strategies.

... but, it works pretty well so far, I think :grinning:

/cc: @jnunemaker, @derekgr