Call to undefined function QueryPath\qp() in QueryPathIterator.php on line 24

If you install QueryPath using composer and use it as follows:

``` php
$qp = \QueryPath::with($string);

$qp->find(':root ul');
```

you'll get the posted error. It seems that the `QueryPathIterator` still relies on the `qp()` function instead of the object oriented interface?
