Following up on #20763, this PR adds support for module- and class-level
docstrings, adds "additional docstrings" as described in [PEP
257](https://peps.python.org/pep-0257/), and fixes function-level
docstrings so that only the first string literal in a function gets
treated as a docstring.
One question that occurs to me is: Would it be good to capture attribute
and additional docstrings differently from regular docstrings? E.g.
`@string.doc.attribute`, `@string.doc.additional`? PEP 257 mentions that
unlike regular docstrings, these docstrings are ignored by the
interpreter (regular docstrings get added as the `__doc__` property of
the object they document), so I can see someone potentially wanting to
style them a little differently.
Release notes:
* Added Python syntax highlighting for class- and module-level
docstrings, additional docstrings, and improved recognition of
function-level docstrings.
Co-authored-by: Piotr Osiewicz <24362066+osiewicz@users.noreply.github.com>
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