Adds zipkin-instrumentation-redis support

[securingsincity]

Closes #27

• Note I didn't include all of the redis commands, but a base set to get started similar to the memcached module

[codefromthecrypt]

food for thought. in finagle, redis is a simple RPC trace with the span.name being the redis command.

so it would be something like:

span.name="append"
annotations="cs","cr" and possibly a "Client Receive Error" pattern

https://github.com/twitter/finagle/blob/develop/finagle-redis/src/main/scala/com/twitter/finagle/redis/filter/RedisTracingFilter.scala
https://github.com/twitter/finagle/blob/develop/finagle-redis/src/main/scala/com/twitter/finagle/redis/protocol/Command.scala

[securingsincity]

@adriancole that's super helpful I'll take a look thanks!