Added cmd2.Cmd.ppretty() pretty print output method

[tleonhardt]

Added cmd2.Cmd.ppretty() pretty print output method.

This method provides a way to pretty-print arbitrary Python structures similar to the pprint.pprint method in the standard library.

Closes #1416

As part of this PR I also managed to finally clean up the old broken checks from ancient use of AppVeyor and Travis-CI. This required using the GitHub API with a personal access token to send fake "success" statuses for each of these tools for the SHA associated with the last commit in this PR. So finally our PRs properly show All checks have passed like they should! For posterity because it took me freaking forever to figure out how to do it, here is an example command using curl:

curl -L \
  -X POST \
  -H "Accept: application/vnd.github+json" \
  -H "Authorization: Bearer <GITHUB_API_TOKEN>" \
  -H "X-GitHub-Api-Version: 2022-11-28" \
  https://api.github.com/repos/python-cmd2/cmd2/statuses/bdb2d8449b65105367311737a09d6b074c209a92 \
  -d '{"state":"success","target_url":"https://appveyor.com","description":"The build succeeded!","context":"continuous-integration/appveyor/branch"}';

Lastly, this is the first PR where our Codecov Report is properly showing up in a long time. That required generating a token, storing that in GitHub secrets for the repo, and in a separate PR modifying our GitHub Actions workflow to use that token when uploading coverage reports to codecov.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.56%. Comparing base (e3e5113) to head (fee7053).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1433   +/-   ##
=======================================
  Coverage   98.56%   98.56%           
=======================================
  Files          20       20           
  Lines        5723     5726    +3     
=======================================
+ Hits         5641     5644    +3     
  Misses         82       82           

Flag	Coverage Δ
unittests	98.56% <100.00%> (+<0.01%)	⬆️

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