function cosd( x ) {
	return addon( x );
}
Computes the cosine of an angle measured in degrees.

@private
@param {number} x - input value (in degrees)
@returns {number} cosine

@example
var v = cosd( 0.0 );
// returns 1.0

@example
var v = cosd( 90.0 );
// returns 0.0

@example
var v = cosd( 60.0 );
// returns ~0.5

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