function cdf( x, x0, gamma ) {
	return addon( x, x0, gamma );
}
Evaluates the cumulative distribution function (CDF) for a Cauchy distribution with location parameter `x0` and scale parameter `gamma` at a value `x`.

@private
@param {number} x - input value
@param {number} x0 - location parameter
@param {PositiveNumber} gamma - scale parameter
@returns {Probability} evaluated CDF

@example
var y = cdf( 4.0, 0.0, 2.0 );
// returns ~0.852

@example
var y = cdf( 1.0, 0.0, 2.0 );
// returns ~0.648

@example
var y = cdf( 1.0, 3.0, 2.0 );
// returns 0.25

@example
var y = cdf( NaN, 0.0, 2.0 );
// returns NaN

@example
var y = cdf( 1.0, 2.0, NaN );
// returns NaN

@example
var y = cdf( 1.0, NaN, 3.0 );
// returns NaN