v0.16.0

This release adds Python 3.10 support, updates bundled libuv to 1.42.0
and fixes a handful of issues.

Changes

• Python 3.10 support (#432)
  (by @elprans in 2519e2d for #432)

• Bump vendored libuv to 1.42.0 (#433)
  (by @elprans in a62f781 for #433)

• Use cibuildwheel to build wheels (#435)
  (by @elprans in 20febe0 for #435)

• Add support for <timer handle>.when()
  (by Jens Jorgensen in 62b2af9)

Fixes

• Fix ref issue when protocol is in Cython
  (by @fantix in 70cafc8 for #2222)

• Set python_requires in setup.py
  (by @graingert in c808a66)

• SSL: schedule first data after waiter wakeup
  (by @fantix in 2081db8)

• Fix a possible race condition in sslproto test
  (by @fantix in b0526cd for #412)

• Fix call_soon_threadsafe thread safety
  (by @fantix in 4b803b1)