Redis driver

#15 Implements [Redis driver spec](https://github.com/pushrax/chihaya/wiki/Implementing-a-driver) with the schema documented in the [wiki](https://github.com/pushrax/chihaya/wiki/Redis-Cache-Schema)

The cache.Tx interface was expanded to simplify testing. Tests & Benchmarks cover all methods in the cache.Tx interface.

Models implements a new method to generate the key for peers in the Seeders and Leecher maps in Torrent types.