function coth( x ) {
	return 1.0 / tanh( x );
}
Computes the hyperbolic cotangent of a number.

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

@example
var v = coth( 0.0 );
// returns Infinity

@example
var v = coth( 2.0 );
// returns ~1.0373

@example
var v = coth( -2.0 );
// returns ~-1.0373

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