Missing docstrings in V4

[StijnKas]

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Issue description

Creating issue for tracking purposes. While refactoring for the V4 version of pdstools, not every class/module/method/function was given docstrings. Now that I've included numpydoc as a pre-commit hook, this becomes an issue. I'd like to use numpydoc to validate new incoming docstrings automatically, but we can't do that today as it's complaining about many missing docstrings instead. This'll be quite some work, but obviously it's necessary to get the API docs up to speed as well.

Reproducible example

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Expected behavior

Unfortunately (for us), every class, method, function should have a docstring, conforming exactly to the numpy docstring standard. I say unfortunately, because this is a lot of work.

Installed versions

V4