function skewness( p ) {
	return addon( p );
}
Returns the skewness of a Bernoulli distribution.

@private
@param {Probability} p - success probability
@returns {PositiveNumber} skewness

@example
var v = skewness( 0.1 );
// returns ~2.667

@example
var v = skewness( 0.5 );
// returns ~0.0

@example
var v = skewness( NaN );
// returns NaN

@example
var v = skewness( 1.5 );
// returns NaN

@example
var v = skewness( -1.0 );
// returns NaN