function identity( x ) {
	return addon( x );
}
Evaluates the identity function for a double-precision floating-point number `x`.

@private
@param {number} x - input value
@returns {number} input value

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

@example
var v = identity( 2.0 );
// returns 2.0

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

@example
var v = identity( -0.0 );
// returns -0.0

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