Issue #17283: Share code between __main__.py and regrtest.py in Lib/test.

This commit also removes TESTCWD from regrtest.py's global namespace.
Issue #16406: Combine the doc pages for uploading and registering to PyPI.
Issue #16406: Combine the doc pages for uploading and registering to PyPI.
Issue #16406: Combine the doc pages for uploading and registering to PyPI.
Closes #17313: Deleted test file created by test_logging.
Fix markup in unittest docs.
Merge markup fixes in unittest docs from 3.2.
Merge markup fixes in unittest docs from 3.3.