针对微信平台新增的事件类型，优化xml解析方法，深度解析xml

例：微信相册发图
<?xml version="1.0" encoding="utf-8"?>
<xml>
  <ToUserName><![CDATA[gh_a73ba7e69f10]]></ToUserName>  
  <FromUserName><![CDATA[oz_amjpBT3uWHby25AHVuwktXh1A]]></FromUserName>  
  <CreateTime>1411837284</CreateTime>  
  <MsgType><![CDATA[event]]></MsgType>  
  <Event><![CDATA[pic_weixin]]></Event>  
  <EventKey><![CDATA[6]]></EventKey>  
  <SendPicsInfo>
    <Count>1</Count>  
    <PicList>
      <item>
        <PicMd5Sum><![CDATA[2505a9ec61478ec9a0edb585f20f3cf0]]></PicMd5Sum> 
      </item> 
    </PicList>  
    <EventKey><![CDATA[btn15]]></EventKey> 
  </SendPicsInfo> 
</xml>