Can use ESC or 'Q' to quit now.

For those who don't know the system shortcut for closing a window.

src/input.cpp

@@ -93,6 +93,9 @@ void input::set_key(SDL_Keysym key, bool value) {
 		case SDLK_d:
 			actions["move_right"] = value;
 			break;
+		case SDLK_ESCAPE:
+		case SDLK_q:
+			actions["quit"] = value;
 		default:
 			break;
 	}