add framerate control (WIP)

src/settings.hpp

@@ -28,6 +28,8 @@ struct DisplaySettings {
     IntegerSetting height {720};
     /// @brief Anti-aliasing samples
     IntegerSetting samples {0};
+    /// @brief Framerate limit
+    IntegerSetting framerate {-1, -1, 120};
     /// @brief VSync on
     FlagSetting vsync {true};
 };