function skewness( a, b, c ) {
	var out;
	if (
		isnan( a ) ||
		isnan( b ) ||
		isnan( c ) ||
		!( a <= c && c <= b )
	) {
		return NaN;
	}
	out = SQRT2 * ( a + b - (2*c) ) * ( (2*a) - b - c ) * ( a - (2*b) + c );
	out /= 5.0 * pow( (a*a) + (b*b) + (c*c) - (a*b) - (a*c) - (b*c), 1.5 );
	return out;
}
Returns the skewness of a triangular distribution.

@param {number} a - minimum support
@param {number} b - maximum support
@param {number} c - mode
@returns {number} skewness

@example
var v = skewness( 0.0, 1.0, 0.5 );
// returns 0.0

@example
var v = skewness( 4.0, 12.0, 9.0 );
// returns ~-0.236

@example
var v = skewness( -4.0, 4.0, -1.0 );
// returns ~0.236

@example
var v = skewness( 1.0, -0.1, 0.5 );
// returns NaN

@example
var v = skewness( 0.0, 1.0, 2.0 );
// returns NaN

@example
var v = skewness( NaN, 4.0, 2.0 );
// returns NaN

@example
var v = skewness( 0.0, NaN, 2.0 );
// returns NaN

@example
var v = skewness( 0.0, 4.0, NaN );
// returns NaN