Python-engineio-v3

- Actively monitor clients for disconnections ([commit](https://github.com/miguelgrinberg/python-engineio/commit/3f583c88449f88200fa5f484954248bfad517aa8))
- parse integer packets as strings [75](https://github.com/miguelgrinberg/python-engineio/issues/75) ([commit](https://github.com/miguelgrinberg/python-engineio/commit/6735659d5cca69476e8a7e98a16a7529ab63a604))
- missing unit test ([commit](https://github.com/miguelgrinberg/python-engineio/commit/a51feef59da8fb491b50a05adb665e980dd9eaa9))
- add Python 3.7 to build ([commit](https://github.com/miguelgrinberg/python-engineio/commit/d9d617a5c62cab692fda4b9664750787303de411))
- removed unused import ([commit](https://github.com/miguelgrinberg/python-engineio/commit/ff3403f1216d838e1930d2322c66bcf609f790e8))
- Tornado docs ([commit](https://github.com/miguelgrinberg/python-engineio/commit/0ef4fbfeeb188a76095de2631cdef9ab4f01839d))

- tornado unit tests ([commit](https://github.com/miguelgrinberg/python-engineio/commit/cb1fe75cea4573dfe3320e5b415c24aaad51d0a0))
- Tornado 5 support ([commit](https://github.com/miguelgrinberg/python-engineio/commit/e0dc7f16c562869d8b48d63f9ee049a413b2f1a2))

- support OPTIONS request method in aiohttp and sanic [70](https://github.com/miguelgrinberg/python-engineio/issues/70) ([commit](https://github.com/miguelgrinberg/python-engineio/commit/27261c7d6563bc5c494e9ff345617a923e17452b))
- More flexible specification of CORS allowed origins Suggested in https://github.com/miguelgrinberg/Flask-SocketIO/issues/697#issuecomment-385203087 ([commit](https://github.com/miguelgrinberg/python-engineio/commit/8f3d6ecff45d474da1a407d654d06fd3f8f882a8))

- basic support for cors allowed headers ([commit](https://github.com/miguelgrinberg/python-engineio/commit/08e3766244b12f704ef20f266f10bdfc7381d43a))
- add pypy3 target to travis builds ([commit](https://github.com/miguelgrinberg/python-engineio/commit/d11b9dae19bf4a5b74b0f6636072e2527a5b8dfe))
- respond to CORS preflight requests [630](https://github.com/miguelgrinberg/Flask-SocketIO/issues/630) ([commit](https://github.com/miguelgrinberg/python-engineio/commit/eac1e516589604a6831f47959047050af23ff01b))

- suppress queue empty errors [65](https://github.com/miguelgrinberg/python-engineio/issues/65) ([commit](https://github.com/miguelgrinberg/python-engineio/commit/861dd52ca2c4fdd9ee1684f1a24bf7acd698039d))

- more aiohttp unit test fixes ([commit](https://github.com/miguelgrinberg/python-engineio/commit/4fd45b8fb86d287c5ba47e7a74cdfb25fa4acb6a))
- fix aiohttp unit test ([commit](https://github.com/miguelgrinberg/python-engineio/commit/4b3ee9309e0250d428fb2faabbb2aa15d377db12))
- support for aiohttp 3.x ([commit](https://github.com/miguelgrinberg/python-engineio/commit/810e759762dd24afa108c8b714fffdced49d3cc1))