Allow preventScroll to be a function?

[brophdawg11]

I was wondering if you would be open to allowing a function to be passed in for preventScroll so the application could make a decision on whether to call preventDefault? I'm still playing around with it a bit, but the current use-case I have is a mobile e-commerce display where there' a main product image that can be swiped left/right to see different images. But setting preventScroll: true makes it such that the user can't scroll by "swiping" up and down on the image either. And when the image takes up most of the vertical real estate, it there's only small sections that the user can use to scroll the image out of the viewport.

I am experimenting locally with using the event details to control whether to preventDefault based on the delta between the x coordinates and y coordinates.

If so, I would be happy to push up a PR once I have something working.