Arcade should make its type hinting available to other modules via PEP 561

Bug Report

Arcade has type hints, but that type hinting information isn't exposed for other modules to use it. See the mypy docs and PEP 561 for more details.

When running mypy against a project that relies on arcade, mypy reports that "arcade" does not provide type hinting:

$ mypy src/
src\myapp.py:4: error: Cannot find implementation or library stub for module named 'arcade'

A project that depends on the arcade package should be able to leverage arcade's type hinting.

A PR is forthcoming...