py-atpublic: updated to 2.1.1

2.1.1:

Rename top-level tests/ directory to test/

2.1:

Clean up some typing problems.
Reorganized docs and tests out of the code directory.
Fix the Windows CI tests.

2.0:

Drop Python 3.4 and 3.5; add Python 3.8 and 3.9.
The C implementation is removed.
Added an @private decorator
Build and test on Windows in addition to Linux.
Fix the doctests so that they actually run and pass!
Add type annotations and API reference documentation.
Internal improvements and modernizations.

(adam)