fix import

fix README

fix: the deadlock on pulling

optimize codes and comment

update readme

update readme

optimize code

socket.Packet: update UnmarshalBody comment

batch update:

1. meta: support ‘X-Accept-Body-Codec’ meta data
2. add 500 CodeInternalServerError Rerror code
3. remove PluginContainer.PreWriteReply and PluginContainer. PostWriteReply’s out args
4. when there is a reply writing error, 500 Rerror code is returned

router: fix unknown pull handler name