function quantile( p ) {
		if ( isnan( p ) || p < 0.0 || p > 1.0 ) {
			return NaN;
		}
		return pow( 1.0 - pow( 1.0-p, 1.0/b ), 1.0/a );
	}
Evaluates the quantile function for a Kumaraswamy's double bounded distribution.

@private
@param {Probability} p - input probability
@returns {number} evaluated quantile function

@example
var y = quantile( 2.0 );
// returns <number>