Added callback for jQuery extension (#601)

Added to the extension for JQuery, callback function.

README.md

@@ -123,10 +123,13 @@ You can also extend jQuery to add a function that does it all for you:
 
 ```javascript
 $.fn.extend({
-    animateCss: function (animationName) {
+    animateCss: function (animationName, callback) {
         var animationEnd = 'webkitAnimationEnd mozAnimationEnd MSAnimationEnd oanimationend animationend';
         this.addClass('animated ' + animationName).one(animationEnd, function() {
             $(this).removeClass('animated ' + animationName);
+            if (callback) {
+              callback();
+            }
         });
         return this;
     }
@@ -137,6 +140,10 @@ And use it like this:
 
 ```javascript
 $('#yourElement').animateCss('bounce');
+or
+$('#yourElement').animateCss('bounce', function () {
+  // Do somthing after animation
+});
 ```
 
 You can change the duration of your animations, add a delay or change the number of times that it plays: