Enum Extend

Provide Derive Macro for Plain Enum

Example

derive EnumStr can impl Some Traits about str and String

1. pub const as_str(&self) -> &'static str
2. AsRef<str>
3. ToString
4. From<&str>
5. From<&String>
6. From<String>

From<Str> Maybe Panic!!!

```rust use enumex::EnumStr;

[derive(EnumStr)]

enum Animal { Cat, Dog, } ```