Improves formatting of docstring + newlines

[northern-64bit]

What does this PR do?

Improve docstrings and kind of standardize them (allowing some variations). It further also makes sure that there is 2 empty rows after and before classes or functions (if they are not a part of a class), and otherwise not.

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• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
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  Pull Request section?

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Anyone in the community is free to review the PR once the tests have passed. Feel free to tag
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[HuggingFaceDocBuilderDev]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

[kashif]

@northern-64bit there might be some potential merge conflicts when #1944 is merged

[northern-64bit]

@northern-64bit there might be some potential merge conflicts when #1944 is merged

Thanks for letting me know. I've now fixed it.

[qgallouedec]

Thanks a lot for cleaning the doc! Please address my comment and we're ready to merge :)