feat: improve watch execution mode

The `watch` command now requires user action to move to the next
exercise.

BREAKING CHANGE: this changes the behavior of `watch`.

exercises/error_handling/errors1.rs

@@ -6,6 +6,8 @@
 // this function to have.
 // Scroll down for hints!!!
 
+// I AM NOT DONE
+
 pub fn generate_nametag_text(name: String) -> Option<String> {
     if name.len() > 0 {
         Some(format!("Hi! My name is {}", name))

exercises/error_handling/errors2.rs

@@ -16,6 +16,8 @@
 // There are at least two ways to implement this that are both correct-- but
 // one is a lot shorter! Scroll down for hints to both ways.
 
+// I AM NOT DONE
+
 use std::num::ParseIntError;
 
 pub fn total_cost(item_quantity: &str) -> Result<i32, ParseIntError> {

exercises/error_handling/errors3.rs

@@ -3,6 +3,8 @@
 // `total_cost` function from the previous exercise. It's not working though!
 // Why not? What should we do to fix it? Scroll for hints!
 
+// I AM NOT DONE
+
 use std::num::ParseIntError;
 
 fn main() {

exercises/error_handling/errorsn.rs

@@ -15,6 +15,8 @@
 //
 // Scroll down for hints :)
 
+// I AM NOT DONE
+
 use std::error;
 use std::fmt;
 use std::io;

exercises/error_handling/option1.rs

@@ -4,6 +4,8 @@
 // on `None`. Handle this in a more graceful way than calling `unwrap`!
 // Scroll down for hints :)
 
+// I AM NOT DONE
+
 pub fn pop_too_much() -> bool {
     let mut list = vec![3];
 

exercises/error_handling/result1.rs

@@ -1,6 +1,8 @@
 // result1.rs
 // Make this test pass! Scroll down for hints :)
 
+// I AM NOT DONE
+
 #[derive(PartialEq, Debug)]
 struct PositiveNonzeroInteger(u64);