add framerate control (WIP)

src/files/settings_io.cpp

@@ -48,6 +48,7 @@ SettingsHandler::SettingsHandler(EngineSettings& settings) {
     builder.add("width", &settings.display.width);
     builder.add("height", &settings.display.height);
     builder.add("samples", &settings.display.samples);
+    builder.add("framerate", &settings.display.framerate);
     builder.add("vsync", &settings.display.vsync);
     builder.add("fullscreen", &settings.display.fullscreen);