Fix some None handling, automate PyPI release

[pjkundert]

This pull merges in some necessary fixes for None handling in wrapped columns, but most importantly:

It automates your PyPI releases, so you don't have to do this manually anymore. The .github/workflow/release.yml pushes any new tagged commit to PyPI.

• Go into your PyPI https://pypi.org/manage/account/publishing/, and add a Github and "Add a new pending publisher" for tabulate referencing the Github astanin python-tabulate repo, and using the release.yml workflow.
• Commit the changes, tag the release with eg. git tag v0.11.0, do a git push (check CI), and a git push --tags to do the PyPI release!

Of course, when you merge, fix everywhere that mentions tabulate-slip39 (my temporary upgrade PyPI shim) back to tabulate:

git grep tabulate-slip39

Other than the wcwidth issues, it should be about ready to release a new official version!

[astanin]

Too many unrelated changes are bundles in a single pull request:

• github workflow changes: not applicable to the upstream
• python 3.8 support changes: should be a separate pr
• None handliong changes