Normalize scrolling speed for Macbook Trackpads and different browsers.

After playing around with this library I found out that it had the same problem as all scrolling libraries have, it behaves completely different in some browsers and especially with macbook trackpads.

After playing around with the scrolling and attempting to fix it myself I found a working piece of code on stackoverflow (http://stackoverflow.com/a/13650579) which I've tested in IE9, IE10, latest Firefox, latest Chrome and in the latest Safari with a normal wheel-based mouse and a macbook trackpad. It works pretty well in my case, but it could still be that I messed something up as I only tested it in a item based slider and as a scrollbar replacement.

But hey, thought you might like it. And thanks for this amazing thing, sly is great!