Inconconsistent docstring for db.parents

[dariober]

There's a tiny inconsistency in the docstring for help(db.parents). Here it reads:

        If `level=None` (default), then return all children regardless
        of level.  If `level` is an integer, then constrain to just that
        level.

It should be something like return all parents regardless... (but I understand that the same docstring serves also db.children).

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Once I'm here... Is there any reason why this PR #237 is not merged in main?