Provides a procedural macro that exposes a compile-time static list of all variants of an enum.
```rust
use enumly::Enumly;
enum Color {
}
assert_eq!(Color::COUNT, 3);
assert_eq!(Color::VARIANTS, &[Color::Red, Color::Green, Color::Blue]);
```
Non-unit variants are rejected at compile time:
```rust
use enumly::Enumly;
enum Bad {
}
```