Syntax to allow multi-line comments that should not become Markdown

[danijar]

This would be useful for docstrings that should be rendered inside the code cell rather than interrupting the document with a Markdown cell. I'm not sure if there is a nice syntax for this so we might decide to not support it, but let's discuss!

[danijar]

Closing this since docstrings are indented except at module-level, so they are already considered code not Markdown. Please comment if treating module-level docstrings as code is an actual use case.