Add docstring for each procedure and method for pelican/__init__.py

[egberts]

Pull Request Checklist

Add missing docstrings to pelican/__init__.py.

Zero code change.

Just a rough cut to see if the Pelican community are up for that. ( I know some folks like comment-less code so treading lightly here).

• Ensured tests pass and (if applicable) updated functional test output
• Conformed to code style guidelines by running appropriate linting tools
• Added tests for changed code
• Updated documentation for changed code

[boxydog]

I am only one voice, and I don't have much influence over whether this gets merged, but ..

I'd be concerned that the long comments would get out of date. Anything that is not unit tested or with eyes on it eventually breaks. For example, the very long comments (e.g., at the top, in __init__, etc.) seem more likely to be out of date to me. So I'd want to hear more about what sort of comments might be likely to remain correct over the long term.

Also, I'd be more interested in type hints, for example. Instead of ":returns None", how about "-> None" on the function signature. Those are also not currently checked, but at least I'd see if they were wrong in my IDE.