bugfix: coroutine pool
introduce socket.channel, and rewrite redis/mongo driver
bugfix: use so:close instead of socket.close
add socket.response to support redis watch mode
bugfix: auth before connected
socketchannel is an independent mod now, channel:request will throw channel.error when disconnected.
bugfix: mongo driver, reply result
Merge branch 'channel' of github.com:cloudwu/skynet into channel