egui demo app

This app demonstrates egui and eframe.

View the demo app online at https://egui.rs.

Run it locally with cargo run --release -p egui_demo_app.

egui_demo_app can be compiled to WASM and viewed in a browser locally with:

./sh/start_server.sh &
./sh/build_demo_web.sh --open

egui_demo_app uses egui_demo_lib.

Running with `wgpu` backend

(cd egui_demo_app && cargo r --features wgpu)