Python-socketio-v4

- SocketIO client
- reorganization of examples, plus some new ones for the client ([commit](https://github.com/miguelgrinberg/python-socketio/commit/4822d8125df11bbf2ef3061c0622164f37a261c9))
- minor example code fix ([commit](https://github.com/miguelgrinberg/python-socketio/commit/fc5fbcf005f750a67d6aeb7bbd190125ea7970fd))
- resolve wrong variable and css element [177](https://github.com/miguelgrinberg/python-socketio/issues/177) ([commit](https://github.com/miguelgrinberg/python-socketio/commit/251b5be9dfc5d88a3bbf146ff52197863d5ce109)) (thanks **iepngs**!)

- Fix variable referenced before assignment [85](https://github.com/miguelgrinberg/python-socketio/issues/85) ([commit](https://github.com/miguelgrinberg/python-socketio/commit/5b9b17c4a0654811aeda4184d159dafb5e0e4041))
- use Python 3.6 for docs build ([commit](https://github.com/miguelgrinberg/python-socketio/commit/142e4787375782c74d6d0b992115269dc290069b))

- update dependencies ([commit](https://github.com/miguelgrinberg/python-socketio/commit/f642a7f2078fc639ed1302b5b3f7133f19c629c6))

- fix backwards compatible problems with python-engineio 3.0 ([commit](https://github.com/miguelgrinberg/python-socketio/commit/fce2006eeef2528e9b59ce9097ff215e6117d787))

- ASGI support ([commit](https://github.com/miguelgrinberg/python-socketio/commit/b214380d056dbbfb08273ac482633254176cb847))
- Fix synchronization issue in SocketIO [213](https://github.com/miguelgrinberg/python-socketio/issues/213) ([commit](https://github.com/miguelgrinberg/python-socketio/commit/4a030d2f9c812b2dd0237883b072189feccac9b7)) (thanks **Anthony Zhang**!)
- Logging improvements for write-only connections [197](https://github.com/miguelgrinberg/python-socketio/issues/197) ([commit](https://github.com/miguelgrinberg/python-socketio/commit/da7cb863301524aead8c4c422491e84c5a1c10bc)) (thanks **Kelly Truesdale**!)
- improved documentation ([commit](https://github.com/miguelgrinberg/python-socketio/commit/87fb830bd803809a6577332a838285b4bc22dce5))
- updated dependencies and fixed linter error ([commit](https://github.com/miguelgrinberg/python-socketio/commit/015ea2037f8fb75c35f8478d14628bf91c54e603))
- better handling of packets with no data ([commit](https://github.com/miguelgrinberg/python-socketio/commit/f2d28ad62caa4ea6374bf9330b4ad7c79eaf2e05))
- add python 3.7 to tox ([commit](https://github.com/miguelgrinberg/python-socketio/commit/1777c527781f788571e4f8a1f8e1f0d813ea9b8b))
- Tornado examples readme ([commit](https://github.com/miguelgrinberg/python-socketio/commit/2a8befdbc9e4fa47a355bf2919319df47b30c973))
- Tornado docs ([commit](https://github.com/miguelgrinberg/python-socketio/commit/415af129b756d5e955180af314589bdc0c5930ff))

- Tornado 5 support ([commit](https://github.com/miguelgrinberg/python-socketio/commit/555b69e80754ceb90d7c7aab1825cc37724b2e90))
- Fix typo in docs [187](https://github.com/miguelgrinberg/python-socketio/issues/187) ([commit](https://github.com/miguelgrinberg/python-socketio/commit/58c8a6f4301758ff27fb95d28b939bf953a67119)) (thanks **Grey Li**!)
- Update documentation link [185](https://github.com/miguelgrinberg/python-socketio/issues/185) Pythonhosted.org was deprecated. ([commit](https://github.com/miguelgrinberg/python-socketio/commit/4131e539f8b480ecd11f0c03239a5359a3012e34)) (thanks **Grey Li**!)
- typo fix [180](https://github.com/miguelgrinberg/python-socketio/issues/180) ([commit](https://github.com/miguelgrinberg/python-socketio/commit/c24c91a72521eeb19eb5ee60e06006da5e8c7578)) (thanks **Toon Knapen**!)
- add pypy3 target to travis builds ([commit](https://github.com/miguelgrinberg/python-socketio/commit/ad37d0db930edf773221cfad40582618c821cb48))