function acoth( x ) {
	return addon( x );
}
Computes the inverse hyperbolic cotangent of a double-precision floating-point number.

@private
@param {number} x - input value
@returns {number} inverse hyperbolic cotangent

@example
var v = acoth( 2.0 );
// returns ~0.5493

@example
var v = acoth( 0.0 );
// returns NaN

@example
var v = acoth( 0.5 );
// returns NaN

@example
var v = acoth( 1.0 );
// returns Infinity

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