eframe app creation refactor (#1363)

* Change how eframe apps are created
* eframe: re-export epi::* so users don't need to care about what epi is

eframe/examples/confirm_exit.rs

@@ -1,6 +1,11 @@
 #![cfg_attr(not(debug_assertions), windows_subsystem = "windows")] // hide console window on Windows in release
 
-use eframe::{egui, epi};
+use eframe::egui;
+
+fn main() {
+    let options = eframe::NativeOptions::default();
+    eframe::run_native("Confirm exit", options, |_cc| Box::new(MyApp::default()));
+}
 
 #[derive(Default)]
 struct MyApp {
@@ -8,17 +13,13 @@ struct MyApp {
     is_exiting: bool,
 }
 
-impl epi::App for MyApp {
-    fn name(&self) -> &str {
-        "Confirm exit"
-    }
-
+impl eframe::App for MyApp {
     fn on_exit_event(&mut self) -> bool {
         self.is_exiting = true;
         self.can_exit
     }
 
-    fn update(&mut self, ctx: &egui::Context, frame: &epi::Frame) {
+    fn update(&mut self, ctx: &egui::Context, frame: &eframe::Frame) {
         egui::CentralPanel::default().show(ctx, |ui| {
             ui.heading("Try to close the window");
         });
@@ -42,8 +43,3 @@ impl epi::App for MyApp {
         }
     }
 }
-
-fn main() {
-    let options = eframe::NativeOptions::default();
-    eframe::run_native(Box::new(MyApp::default()), options);
-}