New feaure request: Adding theorem/proof blocks.

[RootofalleviI]

Hey D2L team,

Thanks for providing us with this great tool!

One small question or feature request: Is it possible to support the functionalities for theorems/proof blocks, e.g., something like this: https://sphinx-proof.readthedocs.io/en/latest/syntax.html?
Maybe this requires defining new syntax in Markdown (e.g., custom tokens for start/end of environments) and translate that into rst.

Thanks!

[RootofalleviI]

I tried to add this line to config.ini:
sphinx_extensions = myst_parser sphinx_proof
which gives me an error:
Extension error: source_suffix '.md' is already registered
which I believe is caused by the extension clash between recommonmark and myst_parser.

Since recommonmark is now deprecated (https://github.com/readthedocs/recommonmark), could we replace it by myst?

Thanks!

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