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/primitive_types/primitive_types1.rs

@@ -2,6 +2,8 @@
 // Fill in the rest of the line that has code missing!
 // No hints, there's no tricks, just get used to typing these :)
 
+// I AM NOT DONE
+
 fn main() {
     // Booleans (`bool`)
 

exercises/primitive_types/primitive_types2.rs

@@ -2,6 +2,8 @@
 // Fill in the rest of the line that has code missing!
 // No hints, there's no tricks, just get used to typing these :)
 
+// I AM NOT DONE
+
 fn main() {
     // Characters (`char`)
 

exercises/primitive_types/primitive_types3.rs

@@ -2,6 +2,8 @@
 // Create an array with at least 100 elements in it where the ??? is. 
 // Scroll down for hints!
 
+// I AM NOT DONE
+
 fn main() {
     let a = ???
 

exercises/primitive_types/primitive_types4.rs

@@ -2,6 +2,8 @@
 // Get a slice out of Array a where the ??? is so that the `if` statement
 // returns true. Scroll down for hints!!
 
+// I AM NOT DONE
+
 #[test]
 fn main() {
     let a = [1, 2, 3, 4, 5];

exercises/primitive_types/primitive_types5.rs

@@ -2,6 +2,8 @@
 // Destructure the `cat` tuple so that the println will work.
 // Scroll down for hints!
 
+// I AM NOT DONE
+
 fn main() {
     let cat = ("Furry McFurson", 3.5);
     let /* your pattern here */ = cat;

exercises/primitive_types/primitive_types6.rs

@@ -3,6 +3,8 @@
 // You can put this right into the `println!` where the ??? is.
 // Scroll down for hints!
 
+// I AM NOT DONE
+
 fn main() {
     let numbers = (1, 2, 3);
     println!("The second number is {}", ???);