Python-socketio-v4

- add async_handlers option to server ([commit](https://github.com/miguelgrinberg/python-socketio/commit/2d39058b7c693bf74c8e3169d72c21a5597d73d8))
- minor class-based namespace fixes ([commit](https://github.com/miguelgrinberg/python-socketio/commit/214abc8d31927673d9b853cf6a901cec1f3988ea))
- minor documentation fixes ([commit](https://github.com/miguelgrinberg/python-socketio/commit/5cc91993369c33ea090782dba1256cce90140295))
- class-based namespaces ([commit](https://github.com/miguelgrinberg/python-socketio/commit/7bc329a12d9f9b4ad4953dc74505167ee4dd5f57))
- minor correction in the readme file example ([commit](https://github.com/miguelgrinberg/python-socketio/commit/6abd86fd868ae4bd5e23b02401f638ec1d0bad2c))
- Update README.rst Add the code highlight to python ([commit](https://github.com/miguelgrinberg/python-socketio/commit/44b1acb6973882be9c89e48e6f187de7aecef8e9)) (thanks **Rodolfo Silva**!)
- add explicit eventlet.wsgi import ([commit](https://github.com/miguelgrinberg/python-socketio/commit/33bd933d8b6c5926c751d6a83f38a2ab7e524b36))
- Handle empty argument list for callbacks [26](https://github.com/miguelgrinberg/python-socketio/issues/26) ([commit](https://github.com/miguelgrinberg/python-socketio/commit/544b01ad3df74cd92199c251292d6a8fdb09f47b))

- minor documentation improvement ([commit](https://github.com/miguelgrinberg/python-socketio/commit/c52f4f6a594f91fc69473d492c0e3117b32de21e))
- Fix race condition in handling of binary attachments [37](https://github.com/miguelgrinberg/python-socketio/issues/37) ([commit](https://github.com/miguelgrinberg/python-socketio/commit/024609e10e570ccd2e932a0584c5a1784c4bbf75))

- Do not allow event names with hyphens in them [36](https://github.com/miguelgrinberg/python-socketio/issues/36) ([commit](https://github.com/miguelgrinberg/python-socketio/commit/a6838a233d051b406baeb9a4c09e50f62bc9f14a))
- add unit test for sleep function ([commit](https://github.com/miguelgrinberg/python-socketio/commit/a3ae2a938472f103d543ad46ff6d923c0f2415ee))

- fix the order of triggered disconnect event [33](https://github.com/miguelgrinberg/python-socketio/issues/33) ([commit](https://github.com/miguelgrinberg/python-socketio/commit/ea1a52ac84cf2cd3d5cb6d1c0f6a64932159d835)) (thanks **Hanzawa Ye**!)
- Correct sio.emit() call in readme [32](https://github.com/miguelgrinberg/python-socketio/issues/32) ([commit](https://github.com/miguelgrinberg/python-socketio/commit/a1ca2c421c4f2f05e83372e4dac0b3826be66d16)) (thanks **winek**!)

- pass return value of start_background_task to the caller ([commit](https://github.com/miguelgrinberg/python-socketio/commit/cd9e1a7c6427eb6e13abea15d84dfc692f843df2))
- a few improvements to examples ([commit](https://github.com/miguelgrinberg/python-socketio/commit/0810f0b039753d9c98f83eebf5a1b183aabd6d49))

- a few improvements to examples ([commit](https://github.com/miguelgrinberg/python-socketio/commit/20185c9a95bcd1ab4d4457b483cf6172eaf020c2))
- expose async_mode and sleep from engineio ([commit](https://github.com/miguelgrinberg/python-socketio/commit/065cc4b2219d22f7b470600073f21c47c09d5578))