Announcing Tornado 6.5.2

[Ben Darnell]

I am pleased to announce the release of Tornado 6.5.2, which is a bug fix release containing five changes:

- Fixed a bug that resulted in WebSocket pings not being sent at the configured interval.
- Improved logging for invalid ``Host`` headers. This was previouisly logged as an uncaught
  exception with a stack trace, now it is simply a 400 response (logged as a warning in the
  access log)
- Restored the ``host`` argument to ``.HTTPServerRequest``. This argument is deprecated
  and will be removed in the future, but its removal with no warning in 6.5.0 was a mistake.
- Removed a debugging print statement that was left in the code.
- Improved type hints for ``gen.multi``.

https://www.tornadoweb.org/en/stable/releases/v6.5.2.html

-Ben