function asin( x ) {
	return addon( x );
}
Computes the arcsine of a double-precision floating-point number.

@private
@param {number} x - input value
@returns {number} arcsine (in radians)

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

@example
var v = asin( 3.141592653589793/4.0 );
// returns ~0.903

@example
var v = asin( -3.141592653589793/6.0 );
// returns ~-0.551

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