Add borderless window mode (from tasks) (#630)

src/settings.hpp

@@ -19,8 +19,8 @@ struct AudioSettings {
 };
 
 struct DisplaySettings {
-    /// @brief Is window in full screen mode
-    FlagSetting fullscreen {false};
+    /// @brief Window mode (windowed/fullscreen/borderless)
+    IntegerSetting windowMode {0, 0, 2};
     /// @brief Window width (pixels)
     IntegerSetting width {1280};
     /// @brief Window height (pixels)