Switch to Markdown-It-Py for Markdown processing

[amykyta3]

Migrate to Markdown-It-Py.
This has a more standardized CommonMark-compliant implementation

Enable the following extensions:

• mdit_py_plugins.admon
• mdit_py_plugins.dollarmath

Since dollarmath has slightly different syntax for inline math (Changes \(...\) to $...$), do this migration for v3.0 of this tool