Support async use-cases

Since we're supporting both python2 and python3, our async options are very limited. I think we have to either use gevent, use threading, or maybe we can use something from the twisted stack?

Personally, I'd really like to just drop support for python2 (it is the way the ecosystem is moving anyway), and use either the 3.4 syntax of @asyncio.coroutine and yield from or 3.5+ of async def and await. It would give us much more semantic code. Maybe the right answer is just a community-maintained async fork for python 3.4+.

Issue created to separate out discussion from #126.

首先阅读这次讨论以及 issue #126，以了解分离的上下文，以及提议的 gevent、threading、Twisted 和 Python 3 asyncio 选项。该 issue 未指出文件、测试或已确定的实现目标；在开始工作之前，需要作出具体决定并制定明确范围的验收标准。