[nostalgia/core] Add key event handler

src/nostalgia/core/glfw/core.hpp

@@ -12,7 +12,9 @@ struct GlfwImplData {
 	struct GLFWwindow *window = nullptr;
 	int64_t startTime = 0;
 	UpdateHandler eventHandler = nullptr;
+	KeyEventHandler keyEventHandler = nullptr;
 	uint64_t wakeupTime = 0;
+	uint64_t keysDown;
 };
 
 }