CircularInterpolation = function(isFlipped) {
            if (isFlipped === undefined) {
              this.isFlipped = false;
            }
          }
@class Implementation of the circular interpolation function.

i = a-(b-a) * (sqrt(1 - (1 - f) * (1 - f) ))
@description The interpolation slope can be flipped to have its steepest ascent
towards the end value, rather than at the beginning in the default
configuration.
@member toxi

@param isFlipped
           true, if slope is inverted