use env_logger in all examples (#2934)

examples/confirm_exit/Cargo.toml

@@ -12,3 +12,4 @@ publish = false
 eframe = { path = "../../crates/eframe", features = [
     "__screenshot", # __screenshot is so we can dump a screenshot using EFRAME_SCREENSHOT_TO
 ] }
+env_logger = "0.10"

examples/confirm_exit/src/main.rs

@@ -3,6 +3,7 @@
 use eframe::egui;
 
 fn main() -> Result<(), eframe::Error> {
+    env_logger::init(); // Log to stderr (if you run with `RUST_LOG=debug`).
     let options = eframe::NativeOptions {
         initial_window_size: Some(egui::vec2(320.0, 240.0)),
         ..Default::default()