Struct ExitCode Copy item path

A special error type that does not print any message when returned from uumain. Especially useful for porting utilities to using UResult.

There are two ways to construct an ExitCode:

use uucore::error::{ExitCode, UResult};
// Explicit
let res: UResult<()> = Err(ExitCode(1).into());

// Using into on `i32`:
let res: UResult<()> = Err(1.into());

This type is especially useful for a trivial conversion from utils returning i32 to returning UResult.