Persisting permalinks in redis.

Redis was selected as storage, for its atomic synchronised increments and performance. Every time someone provides an URL, application will retrieve and increment (both atomically) seed value from Redis. Permalink is generated using that seed (to its unique every time). Incrementing usages count is also trivial using Redis.
Additionally adding guard (for automatically run tests), simplecov (for code coverage tracking), active_attr (to manage attributes of the Permalink model) and figaro (to store configuration parameters of the application).