Refactor the implementation of #[pyclass] and try to let #[pyclass] s…

…upport enum.

There's no functionality since it does not generate __eq__.

Also it only works on enums with only variants, and does not support C-like enums.

pyo3-macros-backend/src/lib.rs

@@ -25,7 +25,7 @@ mod pyproto;
 
 pub use from_pyobject::build_derive_from_pyobject;
 pub use module::{process_functions_in_module, py_init, PyModuleOptions};
-pub use pyclass::{build_py_class, PyClassArgs};
+pub use pyclass::{build_py_class, build_py_enum, PyClassArgs};
 pub use pyfunction::{build_py_function, PyFunctionOptions};
 pub use pyimpl::{build_py_methods, PyClassMethodsType};
 pub use pyproto::build_py_proto;