Add a main menu scene with Start/Hard Mode/Music options

The game now boots into a menu (Start Game, Hard Mode toggle, Music
toggle) navigated with Up/Down and A/Start, instead of dropping
straight into a match. B returns to the menu from a paused or
game-over state.

include/game_render.h

@@ -20,6 +20,7 @@ struct RenderAssets {
 
 void draw_game(const GameState &state, const RenderAssets &assets);
 void draw_stats(const GameState &state, bool internals, bool musicEnabled, uint8_t frame);
+void draw_menu(const GameState &state, const RenderAssets &assets, bool musicEnabled);
 void blink_apples(const GameState &state, u16 *gfx_apple);
 
 #endif