Use single-thread non-blocking asynchronous model w/ Tornado

Thread model of Python w/ version before 3.2 is buggy. See http://www.dabeaz.com/python/GIL.pdf
Also gevent is buggy too. See http://blog.gevent.org/2011/04/28/libev-and-libevent/
So i rewrite the server side code using tornado to solve the related problems.
I'm using this only in Android phones, so i don't have time to rewrite the client-side script.
The PR introduces the dependence of tornado. You can bundle tornado to solve the issue.