Added attr lookup on results via `.get`.

could we change it to 

    return self._d[attr_name]

Seems better to go directly than through another set of indirection, potentially creating an `AttrDict` object and wrapping `KeyError` in `AttributeError` only to throw it away.

Also `.get` is a dict method so perhaps call it `key` instead of `attr_name`? (but that's just me being nitpicky ;)