Add namespace feature SocketIOConnection.

[ghqian]

Reason: When you use url like http://localhost:3000/ the socket.io client will create a websocket transport url like ws://localhost:3000/socket.io. It will work fine. But when you have url like http://localhost:3000/march, then the websocket transport url is also ws://localhost:3000/socket.io but with namespace "/march". And onConnection event in client may need connect signal for namespace "/" and also "/march". After then the emit from server can use namespace "/march" in its packets, and the client will react to namespace "/march" emit.