is_multiple behaviour with 0

[WizardOfMenlo]

Currently, running BigUint::zero().is_multiple_of(&BigUint::zero()) panics, since the implementation attemps to perform a modular division

num-integer/src/lib.rs

Line 888 in d5267dc

*self % *other == 0

However, 0 is indeed a multiple of 0 and as such true should be returned.
Since this is the only edge case, this can be fixed very easily, and I have opened a pull request (#47) accordingly.

[cuviper]

BigUint will have to be fixed in its own implementation in the num-bigint crate.