Misc code cleanup (#3398)

* eframe README: explain how to enable copy/paste

* Implement Debug for a couple of structs

* Code cleanup

* Better docs

* profile ron serialization

* CI: Allow "exclude from changelog" as the only label

crates/egui_demo_app/src/wrap_app.rs

@@ -165,6 +165,7 @@ pub struct WrapApp {
 
 impl WrapApp {
     pub fn new(cc: &eframe::CreationContext<'_>) -> Self {
+        // This gives us image support:
         egui_extras::install_image_loaders(&cc.egui_ctx);
 
         #[allow(unused_mut)]