Intelligently assign class/function docstrings

[agoose77]

Might need a way to disable this with a tag.

This may/may not be useful; a Google-style docstring would naturally work in Markdown, but shouldn't this be left inline with the function definition?

[agoose77]

I have thought more about this, and I think the benefits outweigh the negatives for supporting out-of-definition docstrings. The added readability + Markdown integration improves the use of a notebook rather than detracts from it.

It would be nice to integrate with https://github.com/Carreau/papyri and perhaps generate the appropriate IR from myst-markdown.