feat: basic exercise + functions and mods

src/functions.rs

@@ -91,4 +91,12 @@ pub fn functions_module() {
         my_point.x += x;
         my_point.y += y;
     };
+
+    // Rust provides higher order functions, such as
+    // - map : .map(|n| n * n)
+    // - filter : .filter(|&n| is_add(n))
+    // - take_while : .take_while(|&n| n < upper)
+
+    // Diverging functions
+    // Never return, marked with: !
 }