Scroller seems no used

[ichenhe]

Since Scroller used to calculate current position which relate to the peogress of scrolling. But in this lib we calculate the speed ourselves. Scroller just be used as a flag to indicate whether is scrolling.

So I think we can simply use a boolean var to take the place of the Scroller. I have already done this and every thing woks well.

I am still not sure if you use it for any other reason.