Adding support for isEqual completion handler

[Joebayld]

How hard would it be to add a completion handler for the diff function so the values don't have to be equatable? A library called Diff does this.

For example:

        [1,2,3].diff([3,4,5]) { (old, new) -> Bool in
            return old == new
        }

This would allow me to pass an array of custom models and only check if certain values are equal.

Thanks,
Joe