feat: completed solutions

exercises/21_macros/macros1.rs

@@ -6,5 +6,5 @@ macro_rules! my_macro {
 
 fn main() {
     // TODO: Fix the macro call.
-    my_macro();
+    my_macro!();
 }

exercises/21_macros/macros2.rs

@@ -1,10 +1,10 @@
-fn main() {
-    my_macro!();
-}
-
 // TODO: Fix the compiler error by moving the whole definition of this macro.
 macro_rules! my_macro {
     () => {
         println!("Check out my macro!");
     };
 }
+
+fn main() {
+    my_macro!();
+}

exercises/21_macros/macros3.rs

@@ -1,6 +1,7 @@
 // TODO: Fix the compiler error without taking the macro definition out of this
 // module.
 mod macros {
+    #[macro_export]
     macro_rules! my_macro {
         () => {
             println!("Check out my macro!");

exercises/21_macros/macros4.rs

@@ -3,7 +3,7 @@
 macro_rules! my_macro {
     () => {
         println!("Check out my macro!");
-    }
+    };
     ($val:expr) => {
         println!("Look at this other macro: {}", $val);
     }