Supports the mobile touch scrolling.

Using touch events, support mobile scrolling with touch.

For smooth scroll like browser-default scroll, I implemented stop effect using scrolling speed.

I tested this with my new iPad(3rd generation) and it works nice(I think).

But I don't have any other mobile device, and it's the reason why I made this pull request.

Please test this in several devices and let me know if there's problem.

You can test this patch here: http://perfect-scrollbar-dev.yuiazu.net/

I'll see bugs for several days and when I think it's enough I'll release this.

Thanks!