Generates methods to match enum variant.
```rust use is_variant::IsVariant;
enum TestEnum { A, B(), C(i32, i32), D { _name: String, _age: i32 }, VariantTest, }
fn main() { let x = TestEnum::C(1, 2); assert!(x.is_c());
let x = TestEnum::A;
assert!(x.is_a());
let x = TestEnum::B();
assert!(x.is_b());
let x = TestEnum::D {_name: "Jane Doe".into(), _age: 30 };
assert!(x.is_d());
let x = TestEnum::VariantTest;
assert!(x.is_variant_test());
} ```