Split the game core and ui code into their respective modules

Game state struct ends the variable mess in main.c

game.h

@@ -0,0 +1,19 @@
+#pragma once
+#include <raylib.h>
+
+#define BOARD_WIDTH 4
+#define BOARD_HEIGHT 4
+#define STARTING_TILES 3
+
+typedef enum { UP = 0, DOWN, LEFT, RIGHT } MOVE_DIRECTION;
+
+typedef struct{
+    int board[BOARD_HEIGHT][BOARD_WIDTH];
+    int score;
+    int moves_made;
+} GameState_t;
+
+
+void move(GameState_t *state, MOVE_DIRECTION direction);
+void reset_board(GameState_t *state);
+bool spawn_tile(GameState_t *state);