Replace deprecated gzip with compress_response
Be backwards compatible with tornado 3 for gzip
Test both tornado==3.2.2 and tornado==4.0.2
Use tornado.gen.is_future for checking if result is a Future
tornado 3.x.x does not have tornado.concurrent.is_future
Use generative envlist for tox run
Add Running Tests section to README
Merge pull request #48 from hfaran/develop

Tornado 4.0.x compatibility