Suport for using Redis as cache backend

[kovan]

#7

[kovan]

I have ran the tests using the new AsyncRedisCache with a locally running Redis server, and they all pass

[tractorcow]

I'm using this in an app I'm developing. Only feedback I have is that redis should probably be injectable, in case we are using clustered redis, or requires connection configuration.

[tractorcow]

Thank you so much friend, I can use this module now!