recommonmark is archived and no longer supported

recommonmark is no longer [supported,](https://github.com/readthedocs/recommonmark/issues/221) and [myst-parser](https://pypi.org/project/myst-parser/) is the recommended way forward. I'm happy to work on this with a PR, but I also wanted to start with an issue before pushing up a massive change converting everything from ReST to Markdown.

Begin by reviewing the documentation build configuration and current ReST content to inventory the migration. Replace the archived recommonmark path with myst-parser and convert the project's documentation to Markdown; done means the documentation builds successfully without recommonmark.

Written by the indexing model from the issue text.