Generates methods to print an enum variant's name as a string.
```rust use name_variant::NamedVariant;
#[derive(NamedVariant)] enum TestEnum { A, B(), C(i32, i32), D { _name: String, _age: i32 }, VariantTest, }
fn main() { let x = TestEnum::C(1, 2); asserteq!(x.variantname(), "C");
let x = TestEnum::A;
assert_eq!(x.variant_name(), "A");
let x = TestEnum::B();
assert_eq!(x.variant_name(), "B");
let x = TestEnum::D {_name: "Jane Doe".into(), _age: 30 };
assert_eq!(x.variant_name(), "D");
let x = TestEnum::VariantTest;
assert_eq!(x.variant_name(), "VariantTest");
} ```