Homework:
   1. Implement and run the guessing example.

   $ cat 0101-guessing-game/src/[1]main.rs
   use rand::Rng;
   use std::cmp::Ordering;
   fn main() {
       let secret_number :u32 = rand::thread_rng().gen_range(1..=100);
       let mut guess = String::new();
       loop {
           println!("Guess a number: ");
           guess.clear();
           std::io::stdin().read_line(&mut guess).expect("error reading
   line");
           let guess : u32 = match guess.trim().parse() {
               Ok(num) => num,
               Err(err) => {
                   println!("{}", err);
                   continue
               }
           };
           match secret_number.cmp(&guess) {
               Ordering::Less => println!("Try lower."),
               Ordering::Greater => println!("Try higher."),
               Ordering::Equal => {
                   println!("That's it: {}", secret_number);
                   break;
               }
           }
       }
   }

   2. Make a rust project that uses std::io to generate a .jl julia script
   that performs and outputs the result of an arithmetic calculation.
   file output: [2]https://doc.rust-lang.org/stable/std/io/

   I ended up using [3]https://docs.rust-lang.org/stable/std/fs/

   julia: see other thread with similar name

   $ cat 0102-output-julia/src/[4]main.rs
   use std::io::Write;
   fn main() {
       let mut f : std::fs::File =
   std::fs::File::create("output.jl").expect("failed to create
   output.jl");
       f.write_all(b"x = 4\nprintln(\"4 + 4 = $(x +
   4)\")\n").expect("failed to write lines");
   }
   $ julia output.jl
   4 + 4 = 8

References

   1. http://main.rs/
   2. https://doc.rust-lang.org/stable/std/io/
   3. https://docs.rust-lang.org/stable/std/fs/
   4. http://main.rs/