[guessing-game] more graceful error handling for invalid guess

    // let difference = (guess).abs_diff(secret_number);

    // println!("You guessed {}", guess);

    loop {

        let mut guess = String::new();

        io::stdin()

            .read_line(&mut guess)

            .expect("Failed to read line");

        let guess: u8 = guess.trim().parse().expect("Please type a number");

        let guess: u8 = match guess.trim().parse() {

            Ok(num) => num,

            Err(_) => {

                println!("Please enter a valid guess value.");

                continue;

            },

        };

        println!("You guessed {}", guess);

        match guess.cmp(&secret_number) {

            Ordering::Less => println!("Too small!"),