Release v4.3.29

PYPI: https://pypi.org/project/isbntools/

What's new?

1. Migrate tests to 'pytest'.
2. Fix 'audit' error message.

Release v4.3.28

PYPI: https://pypi.org/project/isbntools/

What's new?

1. Use isbnlib-3.10.9+ to reflect changes in external services.
2. Update docs.