Add convenient project base

src/lib.rs

@@ -0,0 +1,10 @@
+/// Remember the passed value as the solution for the current puzzle.
+/// Prints a specially formatted line so that the solution can be found from the justfile.
+pub fn solved_level_1<S: ToString>(s: S) {
+    println!("level-1-solution={}", s.to_string());
+}
+
+/// See [solved_level_1].
+pub fn solved_level_2<S: ToString>(s: S) {
+    println!("level-2-solution={}", s.to_string());
+}