Upgrade Akka to 2.3 using 2.2 IO pipeline (#65)

Akka IO Pipelines which Redisreact depends on in the network layer
are removed from Akka 2.3 [1]. Since Reactive Stream will take place
of pipelines in Akka 2.4, let's just borrow the old pipeline
implementation for Akka 2.3.

[1] https://groups.google.com/forum/#!topic/akka-user/8fZ75MlVEYc