Derive Error traits for Enum Error struct
```rust
extern crate enumerrorderive;
use std::{io, fmt};
pub enum Error { IO(io::Error), Fmt(fmt::Error), }
fn io_error() -> Result<(), io::Error> { Ok(()) }
fn fmt_error() -> Result<(), fmt::Error> { Ok(()) }
fn mergederror() -> Result<(), Error> { ioerror()?; fmt_error()?; Ok(()) } ```