Added option hook for pillbox to trigger when a item is removed.

Added a option to the pillbox constructor to allow a user to fire off a function when an item is removed. This was useful in a project where I needed to make an AJAX call to delete the items once they were removed from the pillbox.
Thanks
// lance

```javascript
$('#tagBox').pillbox({
	itemRemoved:function(item){
            alert(item.text());
	}
});

```
"Item" is a jQuery instance of the object that was removed. Gives the ability to add an ID to the element.

``` html
<div id="tagBox">
  <ul>
    <li data-id="2" >Item</li>
  </ul>
</div>
```
```javascript
$('#tagBox').pillbox({
	itemRemoved:function(item){
            alert(item.attr('data-id'));
	}
});
```