function haversin( x ) {
	return (1.0 - cos( x )) / 2.0;
}
Computes the half-value versed sine.

@param {number} x - input value (in radians)
@returns {number} half-value versed sine

@example
var v = haversin( 0.0 );
// returns 0.0

@example
var v = haversin( 3.141592653589793/2.0 );
// returns ~0.5

@example
var v = haversin( -3.141592653589793/6.0 );
// returns ~0.06699

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