function cauchy( randn, x0, gamma ) {
	return x0 + ( gamma*tan( PI*( randn()-0.5 ) ) );
}
Returns a pseudorandom number drawn from a Cauchy distribution.

@private
@param {PRNG} randn - PRNG for normally distributed numbers
@param {number} x0 - location parameter
@param {PositiveNumber} gamma - scale parameter
@returns {number} pseudorandom number