add R key to restart game

js/keyboard_input_manager.js

@@ -61,6 +61,11 @@ KeyboardInputManager.prototype.listen = function () {
         self.emit("move", mapped);
       }
     }
+
+    // R key restarts the game
+    if (!modifiers && event.which === 82) {
+      self.restart.call(self, event);
+    }
   });
 
   // Respond to button presses