文章：http://www.jianshu.com/p/40d8bc17529f
socket.io提供rooms和namespace的API 用rooms的API就可以实现多房间聊天了，总结出来无外乎就是：join/leave room 和 say to room
// join和leave
io.on('connection', function(socket){
socket.join('some room');
// socket.leave('some room');
});
// say to room
io.to('some room').emit('some event'):
io.in('some room').emit('some event'):
