Migrating from 0.19 to 0.19

Observer overhaul

TransitionListener has been deleted, use observers instead:

> app.add_observer(
>     |trigger: On<LoadingCompleted>| println!("do stuff"),
> );
< active_machines.push_listener::<ReloadingInitialized<P>>(OnLoadingCompleteListener);

This allows you to use more convenient system parameter syntax to access resources and queries, but you may not use exclusive systems anymore.

If you want observers to respect ordering between themselves, you should prefer to issue commands in these instead (see related bevy issue).

Renaming Reflection Rroxies

Val<T>, Ref<T> and Mut<T> have been renamed to prevent clashes with native bevy types, as well as save a few keystrokes.

You should use: V<T>, R<T> and M<T> instead

> V<T>
< Val<T>

> R<T>
< Ref<T>

> M<T>
< Mut<T>

ScriptValue::List changes

This variant now uses VecDeque instead of Vec