Migrate documentation to use Markdown and MkDocs

[tleonhardt]

Migrate documentation to use MkDocs with the Material Theme for the build. Replaced all use of reStructuredText with Markdown and all use of Sphinx with MkDocs.

TODO:

• Create MkDocs Material theme basic setup and configuration
• Translate reStructuredText docs to Markdown using pandoc
• Verify MkDocs build and serve are working
• Delete Sphinx stuff and make sure GitHub Actions doc build is working
• Finish correcting basic translation errors
• Get automated API documentation using mkdocstrings working nicely
• Figure out how to do autodoc references using mkdocstring
• Final cleanup check of markdown
• Make recommended tweaks for hosting docs on ReadTheDocs
• Add example of using mermaid to embed diagrams in scripting.md
• Verify ReadTheDocs build is working properly

Closes #1396

[tleonhardt]

@kotfu @kmvanbrunt This PR is now ready for your review. Everything appears to work and I'm happy with the way it looks. I think there is a tremendous amount of room for further improvement down the road given the overall capabilities of the MkDocs Material Theme, but this seems like a great start.

[tleonhardt]

The docs this PR generates can be viewed as built by ReadTheDocs here.

They are fully working other than the search - ReadTheDocs serves PR builds from a different domain than normal which is why I think that is broken. It should work in an actual build off the master branch.

There is a little button in the top center that looks like a sun or moon which you can use toggle between dark and light mode and your browser will remember the setting for the same page if viewed again.