Hi:
All contributors and committers!
after consideration about rocketmq client go design, I have some
special ideas about client: out-of-order submit、various
consuming mode、goroutine-pool、explicit error code、batch model and so on.more detail refer by https://docs.google.com/document/d/1SovDAthbiD66x4hu5KflEF0Kc8WPnK3sC5ztf8FIdBU/edit#
