Moved off of `keys` to support `twemproxy`. Fixes #7

We have a timebomb waiting for us with regard to using `keys` and `twemproxy`, as `keys` is not supported. This PR fixes that by moving off of `keys` and onto a `set` for tracking hashes.

https://github.com/twitter/twemproxy/blob/v0.3.0/notes/redis.md

http://redis.io/commands#set

In this PR:

- Remove pattern notion from `backbone-api-client-redis`
- Add `hash` redis keys for models and collections
- Save `object-hash` to hash key on uncached get
- Fetch/delete `object-hash` redis keys on cache clear

/cc @mlmorg @Raynos