Support renaming enum variants

[DataTriny]

It would be really convenient if the #[pyclass] attribute offered a way to rename all variants of an enum.

The problem

By default the generated Python enums expose variants named after Rust's naming convention, which is not idiomatic for Python where SCREAMING_SNAKE_CASE is the norm. One can either create a new enum specifically tailored for PyO3, or apply #[pyo3(name = "...")] to every variants. Neither of these options are practical for big enums, and I can't make the second one work if I need to conditionally support PyO3: #[cfg_attr(feature = "pyo3", pyo3(name = "...")] won't compile.

Solution

Add a new argument to #[pyclass] that would only apply to enums and that would rename all their variants: rename_all for instance.

It could be a good idea to also support #[serde(rename_all = "...")] if it is already applied to an enum, although I don't think it would happen often that people use screaming snake case when (de)serializing their types.