Using attribute dicts does not work with dicts within lists

Here is a fix. Check if there are other problems cause by this.

``` python
    def _use_attrdicts(self, obj):
        if isinstance(obj, dict):
            obj = {k: self._use_attrdicts(v) for k, v in obj.items()}
            return AttrDict(obj)
        elif isinstance(obj, list):
            return [self._use_attrdicts(x) for x in obj]
        return obj
```
