Add missing return statements to example inputs

examples/agecontrol/agecontrol.mc

@@ -25,4 +25,5 @@ int main()
 		print("You Can Drink!");
 	}
 	print_nl();
+	return 0;
 }

examples/is_square/is_square.mc

@@ -27,4 +27,5 @@ int main()
 		print("No");
 	}
 	print_nl();
+	return 0;
 }

examples/slowsort/slowsort.mc

@@ -148,5 +148,5 @@ int main(){
         print_f_array(f_arr, arr_size);
     }
 
-	return 0;
+    return 0;
 }