A simple derive macro to generate an ordinal() method for enums.

Unlike num_derive::ToPrimitive, this derive macro allows non-C-like enums. The ordinal function reflects the variant of the enum and does not account for fields.

Example

use ordinalizer::Ordinal;
#[derive(Ordinal)]
enum Animal {
    Dog,
    Cat {
        age: i32,
    }
}

assert_eq!(Animal::Dog.ordinal(), 0);
assert_eq!((Animal::Cat { age: 10 }).ordinal(), 1);