Always round x and y coordinates when using mousewheel

This addresses all of the blurriness on scroll issues, e.g. #197

Up until now, the best solution I could find to this problem was to disable 3d transforms using the useTransform option. This forced the _translate method to round the coordinates. However, this came at the cost of moving the translation off of the HW. The resulting performance is horrendous on mobile devices.

By always rounding coordinates, we nullify the blurring problem without the performance hit of software animation.