Added scrollResistance option

When I enabled the slimScroll feature on my project, I noticed that it pretty sucks when you reach the scrollable area's end, the fullPage automatically slides down.
So I added the scrollResistance option. With this option you can regulate at which "strength" of scrolling the section-slide occurs.
The default is one and each +120 is +1 'click' on the mousewheel.
Please review and pull ;)