Move systems into subdirectory, add tree shake animation

CMakeLists.txt

@@ -9,6 +9,14 @@ add_subdirectory(engine/)
 
 
 add_executable(PixelDefense
+        game/systems/s_ai.c
+        game/systems/s_animation.c
+        game/systems/s_entity.c
+        game/systems/s_event.c
+        game/systems/s_input.c
+        game/systems/s_ui.c
+        game/systems/systems.h
+
         game/buildings.c
         game/buildings.h
         game/components.c
@@ -23,11 +31,6 @@ add_executable(PixelDefense
         game/map_layers.h
         game/pathfinding.c
         game/pathfinding.h
-        game/systems.h
-        game/systems_ai.c
-        game/systems_entity.c
-        game/systems_input.c
-        game/systems_ui.c
         game/ui_widgets.c
         game/ui_widgets.h
         game/unit_actions.c