Feature Request: `cancel` method

[brandonmcconnell]

It would be great to have a method to call to forcibly cancel a scroll that has already been initiated using scroll-js. This way, if a user starts manually scrolling or performs a pointer/touch event during the scroll, I can cancel the scroll to freeze the frame at the time they trigger that event.

This would be similar to the cancelScroll method from @cferdinandi's smooth-scroll package.