Move wrap_pyfunction into prelude?

[Eric-Arellano]

Hello! We're using wrap_pyfunction a lot in pantsbuild/pants, and found we prefer #[pyfunction] over #[pyfn] to keep our #[pymodule] block clean. (I'm submitting a docs PR on other things we've found to help.)

I'm wondering if it makes sense to move the macro into the prelude, given how common this type seems to be, for fewer imports? Maybe the create_exception macro too?

I'm happy to implement if you think so!

[davidhewitt]

I would definitely support wrap_pyfunction being in the prelude. It's very commonly used.

I would prefer not to add create_exception for now, only because we plan to eventually replace it (#295).