Merge pull request #15 from cowboy129/master

Add serializer benchmark
Simplified method names.
final serializer's methods for performance.
Added broadcast load test for cluster.
Comments.
Removed unused JsonRender
Extracted fixed parts of XhrPolling.
Moved class LocalMediator to LocalConnectionActive.scala
One OnData channel is enough.
Updated example code.
Exposed channel of Namespace to observer.
Tried to construct a type aware Observable[OnEvent] via flatMap.
Decoupling busi nodes and conn/tran nodes.

1. move busi nodes out of the socketio cluster
2. busi nodes will register themselves to the cluster, and the cluster use ClusterNamespaceMediator to route (by RoundRobin etc.) OnPacket msg to one of the busi nodes within the same group (same system name).