ExponentialInterpolation = function(exp) {
            this.exponent = exp === undefined ? 2 : exp;
          }
@class Exponential curve interpolation with adjustable exponent. Use exp in the
following ranges to achieve these effects:
<ul>
<li>0.0 &lt; x &lt; 1.0 : ease in (steep changes towards b)</li>
<li>1.0 : same as {@link LinearInterpolation}</li>
<li>&gt; 1.0 : ease-out (steep changes from a)</li>
</ul>
@member toxi