基于xmpp协议的client端引擎的实现。包括基本的login、roster列表的获取、message的收发、presence的发送和接收处理，以及subscribe/subscribed的实现。-Xmpp agreement based on client-side engine to achieve. Including the basic login, roster list of access, message and delivery, presence of the sending and receiving, as well as subscribe/subscribed realized.