function csch( x ) {
	return 1.0 / sinh( x );
}
Computes the hyperbolic cosecant of a number.

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

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

@example
var v = csch( 2.0 );
// returns ~0.2757

@example
var v = csch( -2.0 );
// returns ~-0.2757

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