function quantile( p, c ) {
	if (
		isnan( c ) ||
		isnan( p ) ||
		c <= 0.0 ||
		p < 0.0 ||
		p > 1.0
	) {
		return NaN;
	}
	return expm1( p * log1p( c ) ) / c;
}
Evaluates the quantile function for a Bradford distribution with shape parameter `c` at a probability `p`.

@param {Probability} p - input value
@param {PositiveNumber} c - shape parameter
@returns {NonNegativeNumber} evaluated quantile function

@example
var y = quantile( 0.1, 0.1 );
// returns ~0.096

@example
var y = quantile( 0.5, 5.0 );
// returns ~0.290

@example
var y = quantile( 1.0, 10.0 );
// returns 1.0

@example
var y = quantile( 0.5, 0.0 );
// returns NaN

@example
var y = quantile( 2.0, 0.5 );
// returns NaN

@example
var y = quantile( -1.0, 0.5 );
// returns NaN

@example
var y = quantile( NaN, 1.0 );
// returns NaN

@example
var y = quantile( 1.0, NaN );
// returns NaN