Rename crate::events to crate::messages

Bevy 0.17 introduces this idea of "Messages" which mostly replace the
previous usage of "Events." The old events still exist, but are meant
more for targetted actions -- something happening and immediately
triggering a function call on an observer.

src/machinery.rs

@@ -8,7 +8,7 @@ use std::time::Duration;
 
 use bevy::prelude::*;
 
-use crate::{WorldSize, events::{AsteroidDestroy, SpawnAsteroid}, objects::AsteroidSize, resources::Score};
+use crate::{WorldSize, messages::{AsteroidDestroy, SpawnAsteroid}, objects::AsteroidSize, resources::Score};
 
 /// Asteroid spawning parameters and state.
 ///