- Added public `Error`, `Result`, `InitFuture`, and `ShutdownFuture`
aliases.
- Added `TypeMapState` as the default state instead of `Arc<TypeMap>`.
- Added `App::route`, `App::mount`, and `App::store`.
- Changed `App::init()` to return `InitializedApp<S>`.
- Added `InitializedApp::router()`, `state()`, `into_parts()`, and
`shutdown()`.
- Made shutdown hooks fallible: `Result<()>`.
- Made `AdHocPlugin::on_shutdown` accept capturing closures.
- Added `Default` for `App` and `AdHocPlugin`.
Improved AppState macro:
- Uses `axum_app_wrapper::Error`.
- Supports generic state structs.
- Fixed the stale `Arc<AppState>` doc snippet.
