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/macros/macros1.rs

@@ -1,6 +1,8 @@
 // macros1.rs
 // Make me compile! Scroll down for hints :)
 
+// I AM NOT DONE
+
 macro_rules! my_macro {
     () => {
         println!("Check out my macro!");

exercises/macros/macros2.rs

@@ -1,6 +1,8 @@
 // macros2.rs
 // Make me compile! Scroll down for hints :)
 
+// I AM NOT DONE
+
 fn main() {
     my_macro!();
 }

exercises/macros/macros3.rs

@@ -1,6 +1,8 @@
 // macros3.rs
 // Make me compile, without taking the macro out of the module! Scroll down for hints :)
 
+// I AM NOT DONE
+
 mod macros {
     macro_rules! my_macro {
         () => {

exercises/macros/macros4.rs

@@ -1,6 +1,8 @@
 // macros4.rs
 // Make me compile! Scroll down for hints :)
 
+// I AM NOT DONE
+
 macro_rules! my_macro {
     () => {
         println!("Check out my macro!");