A bit clunky on right to left drag with few images

[Laz75]

Hello, I was trying to use this great script with a lower number of images (15-20) and noticed that dragging from right to left was a bit clunky (while left to right worked beautifully.

I realized the problem was the Math.ceil used in the trackPointer function, with negative numbers it doesn't produce the expected output (this doesn't occur when you're using many more images, of course).

A simple if using Math.floor for negative numbers does the trick and everything works just fine now.

if (pointerDistance > 0) {
endFrame = currentFrame + Math.ceil((totalFrames - 1) * speedMultiplier * (pointerDistance / $container.width()));
} else {
endFrame = currentFrame + Math.floor((totalFrames - 1) * speedMultiplier * (pointerDistance / $container.width()));
}