http://www.cnblogs.com/ajccom/archive/2013/07/18/3197809.html
http://*.com/questions/10058226/send-response-to-all-clients-except-sender-socket-io
http://cnodejs.org/topic/4feb37348a7cb2d22b4edf96
https://github.com/leizongmin/qchat/blob/master/lib/room.js