that will be used by get_op_params() to
auto-generate macros for the op.

Add two methods to help create enums quickly.

Add a test for this new feature.

Simplify code.

Add new op param types `EnumType` and `EnumList`.

This replaces the previous implementation.

C macros are created into `EnumType.c_support_code()`.

Examples added in gof/tests/test_types.

Flake8.