Bindings for super()

[davidhewitt]

I don't think PyO3 currently exposes an API to get super() from Rust.

As far as I'm aware there aren't special C APIs to call super(), instead I think ffi::PySuper_Type can be cast to &PyType and we can then use .call1((type, obj)) to fill in the arguments. I think we'd always need to use the two-argument form as I don't think the PEP 3135 syntax sugar can apply here.

Some ideas what could be done:

• Add a PySuper type to pyo3::types, with constructors like PySuper::new(ty: &PyType, obj: &PyAny) -> PyResult<PySuper>
• Maybe add PyAny::super() which calls PySuper::new with the object and its type for convenience.