使WxRequest的构造参数中的xml不是必选，方便测试
实现服务端API接口
修复send_message的bug
发布0.3.1
支持非继承式使用wxApplication，设置app的handlers即可
add on_voice  on_video
Merge pull request #1 from Yemsheng/develop

add on_voice  on_video
upgrade to 0.3.2
Merge branch 'release/0.3.2'