Saved the user's success callback. 

It wasn't enough for me to observe "pjax:success" or "pjax:complete" events, so I just tweaked the code a bit to save the "success" function if it's passed in and then call it after the firing the pjax event. Doubt it's the best way but really needed a way to be able to add a callback. 

So essentially, now I'm able to add a callback per pjax call like so...

```javascript
$.pjax({url: "someurl", 
 "container": "#container", 
 "success" : function(data, status, xhr, options){
    // do something here...
 });
```