ClassRegistry v4.0.5

[todofixthis]

This version fixes some issues with project metadata; there are no functional changes in this release.

• Fixed Tox configuration — it now ACTUALLY runs the unit tests 😅
• Renamed unit tests to match unittest discoverer's default pattern (test_*.py).
• Fixed an issue preventing unit tests from getting included in sdist builds.
• Added instructions to run unit tests outside of Tox.
• Added bug tracker to project links.
• Removed reference to discontinued travis-ci.org.
• Tightened up disclaimers in documentation.