Provides extension to rust enum

This crate provides Enumeration trait for rust enum with the following features - implementation for common traits (Clone, Copy, Hash, etc.) - getting number of variants through constant Enumeration::VARIANT_COUNT - casting between index (of type Enumeration::Index) and enumeration - attaching a constant value to each of the variants - runtime representation of enumeration

```rust use enumeration::{prelude::*, OutOfRangeError};

enumerate!(pub Foo(u8; i32 = 11) Bar Baz = 99 );

pub fn main() -> Result { asserteq!(Foo::Bar, Foo::variant(0)?); asserteq!(Foo::Baz.toindex(), 1); asserteq!(Foo::Bar.value(), 11); assert_eq!(Foo::Baz.value(), 99);

let variants: Vec<Variant<_>> = vec![Foo::Bar.into(), SomeOtherExternalEnum::SomeVariant.into()];

assert_eq!(variants[0].cast::<Foo>(), Ok(Foo::Bar));
assert_eq!(variants[1].cast::<SomeOtherExternalEnum>(), Ok(SomeOtherExternalEnum::SomeVariant));
assert!(variants[1].cast::<Foo>().is_err());

} ```