- updated to work with Tornado 5, which is now the minimum required version
- require pytest >= 3.0
- the io_loop fixture always refers to a tornado.ioloop.IOLoop instance now
- the io_loop_asyncio and io_loop_tornado fixtures have been removed, since now that Tornado 5 always uses asyncio under Python 3, there would be no difference between the two fixtures, so io_loop is all that is needed
- tox tests now test more versions of Tornado (5.0.* and latest 5.*), Pytest (3.0.* and latest 3.*), and Python (3.5, 3.6, 3.7, and pypy3).