Added callback to destroy

Added a callback function to the destroy method for simple chaining.

jquery.isotope.js

@@ -836,7 +836,7 @@
     },
 
     // destroys widget, returns elements and container back (close) to original style
-    destroy : function() {
+    destroy : function( callback ) {
 
       var usingTransforms = this.usingTransforms;
       var options = this.options;
@@ -868,6 +868,9 @@
 
       $window.unbind('.isotope');
       
+      if ( callback ) {
+        callback();
+      }
     },