move applcation callback declarations to game_api.h to ease warnings

src/game_api.h

@@ -8,7 +8,8 @@
 #include "audio.h"
 #include "util.h"
 
-#include <SDL2/SDL.h>
-
+/* application provided */
+extern void game_tick(void);
+extern void game_end(void);
 
 #endif

src/main.c

@@ -3,6 +3,7 @@
 #include "input.h"
 #include "util.h"
 #include "textures.h"
+#include "game_api.h"
 #include "audio/internal_api.h"
 
 #include <SDL2/SDL.h>
@@ -19,11 +20,6 @@
 #include <limits.h>
 
 
-/* application provided */
-extern void game_tick(void);
-extern void game_end(void);
-
-
 static void poll_events(void) {
     SDL_Event e;