Attempt to add gamepad support.

game.js

@@ -34,7 +34,13 @@ window.addEventListener("load", async () => {
           addEventListener: (target, type, listener) => target.addEventListener(type, listener),
           removeEventListener: (target, type, listener) => target.removeEventListener(type, listener),
           preventDefault: (event) => event.preventDefault(),
-          keyboardCode: (event) => event.code
+          keyboardCode: (event) => event.code,
+          gamepad: (event) => event.gamepad
+        },
+        gamepad: {
+          index: (gp) => gp.index,
+          button: (gp, i) => gp.buttons[i] || null,
+          buttonPressed: (b) => b.pressed
         },
         image: {
           new: (src) => {