We can remove the C stack use and general overhead of calling special methods implemented in Python for attribute access and indexing.

Each operation has a special method that implements it. When that special method is implemented in Python, we should avoid the `tp_xxx` slot machinery and use the same mechanism we use for normal calls to Python functions. 

* BINARY_SUBSCR: `__getitem__`
* STORE_SUBSCR: `__setitem__`
* LOAD_ATTR: `__getattribute__` (and maybe `__getattr__`)
* STORE_ATTR: `__setattr__`

It probably isn't worth bothering with the deletion forms.

The getters (`__getitem__` and `__getattribute__`) are relatively simple, as the call returns the result.

The setters are a bit more complicated as the return value needs to be discarded, so an additional frame which discards the result of the call needs to be inserted.