[3.8] bpo-38148: Add slots to asyncio transports (GH-16077) (GH-16093)

* bpo-38148: Add slots to asyncio transports

* Update Misc/NEWS.d/next/Library/2019-09-13-08-55-43.bpo-38148.Lnww6D.rst

Co-Authored-By: Kyle Stanley <aeros167@gmail.com>
(cherry picked from commit 9eb35ab0d71a6bd680e84fa0f828cb634e72b681)

Co-authored-by: Andrew Svetlov <andrew.svetlov@gmail.com>
3 files changed