Update jquery.slimscroll.js to allow simple animated scrolls.

Hello - I'm new to github, so 
a) I apologize if I'm going about this wrong (feel free to berate me) and 
b) I hope this is in some way helpful/its something you think would be helpful to other people. 

I added the ability for slimScroll to allow for animated scroll calls.  All one would have to do is add an animate option to their call.. eg.

$("#thing-to-scroll").slimScroll({ scrollTo: scrollLocation, animate: true });