Implements `asyncio.to_thread`, a coroutine for asynchronously running IO-bound functions in a separate thread without blocking the event loop. See the discussion starting from [here](https://github.com/python/cpython/pull/18410GH-issuecomment-628930973) in GH-18410 for context.
Automerge-Triggered-By: @aeros
(cherry picked from commit cc2bbc2227)
Co-authored-by: Kyle Stanley <aeros167@gmail.com>
* This just copies the docs from `StreamWriter` and `StreamReader`.
* Add docstring for asyncio functions.
https://bugs.python.org/issue36889
Automerge-Triggered-By: @asvetlov
Miss Islington (bot)
Yury Selivanov
Xtreak
Yury Selivanov