Changelog:

• Add tox tests
• Add PEP 613 TypeAlias
• Add SupportsIndex, added in Python 3.8
• Fix required and optional keys inheritance for TypedDict
• Replace asyncio.coroutine with async-await
• Reuse stdlib PEP 593 implementation in typing_extensions if present
• Backport get_origin() and get_args()
• Track optional TypdeDict keys
• Accept arbitrary keyword names in NamedTuple() and TypedDict()

Signed-off-by: Algent Albrahimi <algent@protonmail.com>

Update python-mypy against this version and check for errors with it in some python scripts.