Adding a new parameter: _precision.

The interpolation of values could result in values with decimals of an extremely long length, e.g. 'width: 50.12345678901%'.  Since scrolling causes browser repaints, which will be impacted by updated CSS values, performance can be negatively impacted.

I'm proposing a new init option: _precision. This will be used to limit the interpolated value returned from _calcInterpolation via the toFixed(n) method.  The default will be 10 (which is likely more than enough for most use-cases) or the user-specified value.