Cubic Interpolation Support

The removablePositions ArrayList, and the way getCurrentPosition() worked did not work well in the case of needing more than the current and next points.

Support for cubic Interpolation has been added, but needed the previous, current, next, and after next, points and major changes to the getCurrentPosition() method were required.
Cubic Interpolation Support
Extra paramater for smooth (cubic) interpolation
Forgot to make the smoothing option unnecessary

- Defaults to non-smooth
Merge pull request #4 from Olhcim/master

Cubic Interpolation