Merge pull request #9 from cowboy129/master

Add test for cluster broadcast
Added broadcast in load test.
Varies fixed for broadcast load test.
Distinct endpoint and namespace carefully in Namespace.
Added apply method for LocalNamespace and ClusterNamespace to simplify
namespace subscribe.
Implemented server-side ack.
Fixed AckPacket match error in ConnectionActive.onPacket;
Added basic ack feature for SocketIOClientConnection.
Add SimpleClusterServer