Enhancement: `to_dict` method

[Goldziher]

Hi there,

Thanks for this library. I'd like to ask for a convenience method that output a dict of a multidict - with lists for multi-values. Currently I have this:

    def dict(self) -> Dict[str, List[Any]]:
        """

        Returns:
            A dict of lists
        """
        return {k: self.getall(k) for k in set(self.keys)}

While this works, its not very performant.

[asvetlov]

Hey!
I doubt if it can be faster if implemented in C.
Did you try to implement the proposed method?
Do you have any performance numbers?