Created a combat system to start with and also added a 'HEARING' mechanic where enemies can hear you from a certain distance before moving to you.

gui.cpp

@@ -164,6 +164,7 @@ void GUI::run_systems() {
   System::enemy_pathing($world, $game_map, player);
   System::motion($world, $game_map);
   System::combat($world, player);
+  System::death($world);
 }
 
 void GUI::resize_map(int new_size) {