infinite recursive when dictionary has array of dictionary refer to the parent.

for example:
```
>>> import box
>>> a={'a': 1}
>>> a['b'] = [{'parent': a}]
>>> box.Box(a)
Traceback (most recent call last):
...
RecursionError: maximum recursion depth exceeded in __subclasscheck__

```
any idea? how to implement the data structure like this?
Thanks!