Expose `bin_name` after parsing

[yanganto]

Hi here,

It is awesome to see a Rust argument framework to give developer more power to control the argument in details and in a powerful way. A small issue is found, the bin_name is hidden (not shown in the operands) after argument parsing.

Some application may use bin_name as a command selector to execute different functions, so following is a propose. If this looks good, I can make a PR for this.

let (s, bin_name, operands) = Settings::default().parse(args).unwrap();

This project is fresh new for me, if I miss something please kindly let me know. 🙏

[tertsdiepraam]

That's correct and would be a nice addition!