Tornado 4.3b1，支持 async/await 关键字

Highlights

• The new async/await keywords in Python 3.5 are supported. In most cases, async def can be used in place of the @gen.coroutine decorator. Inside a function defined with async def, use await instead of yield to wait on an asynchronous operation. Coroutines defined with async/await will be faster than those defined with @gen.coroutine and yield, but do not support some features including .Callback/.Wait or the ability to yield a Twisted Deferred.
• The async/await keywords are also available when compiling with Cython in older versions of Python.

Deprecation notice

• This will be the last release of Tornado to support Python 2.6 or 3.2. Note that PyPy3 will continue to be supported even though it implements a mix of Python 3.2 and 3.3 features.

更多的请看：http://www.tornadoweb.org/en/latest/releases/next.html

不知道 asyncio 的库是不是可以直接用在 Tornado 上面了，如果可以我就升到 3.5 了....