update for chat demo
add some code for demo
Merge pull request #1 from lbt05/chat-group

Chat group
Merge pull request #13 from lbt05/master

新聊天demo
由于更新消息格式导致的receiver接口变化
update code to AVGroup interface
Merge pull request #2 from lbt05/chat-group

Chat group
Merge pull request #14 from lbt05/master

V2.6.2
Merge remote-tracking branch 'upstream/master'