Description: Sets the notification message contents

Parameters:

@content {String or DOMElement} The notification message content

 var duration = 10;
 var msg = alertify.message('Auto-dismiss in '+ duration +' seconds.', 10, function(){ clearInterval(interval);});
 var interval = setInterval(function(){
    msg.setContent('Auto-dismiss in '+(--duration)+' seconds.');
 },1000);