Add iPhone compatibility.
Handle pan better with relative (instead of absolute) positioning.

With the old code, the range would jump so that your touch is in the
center of the range. With this change, the selected range moves
according to the distance you move your touch, which is more natural
and intuitive.
Merge pull request #4 from intelliot/handlePanBetter

Handle pan better with relative (instead of absolute) positioning
Merge pull request #1 from sammyd/master

Pulling updates from sammyd/master