Add AngularVelocity, begin removal of Rotation

The rotation component is also redundant with Bevy's transform
component.

This new component and system fill the physics role, but the input
handling code needs to be updated.

Player steering still functions because it uses the `Rotation` component
to direct the force vector. The force is correctly applied to the linear
velocity vector. An improvement would be to have a force/impulse
accumulator so I could account for mass, but I'm not going to do that
right now.

src/physics.rs

@@ -26,12 +26,15 @@ pub(crate) fn integrate_velocity(mut query: Query<(&mut Transform, &Velocity)>,
     }
 }
 
-/*
- Assigns the rotation to the transform by copying it from the Rotation component.
-*/
-pub(crate) fn apply_rotation_to_mesh(mut query: Query<(&mut Transform, &Rotation)>) {
-    for (mut transform, rotation) in &mut query {
-        transform.rotation = Quat::from_rotation_z(rotation.0);
+/// Integrate angular velocity and update the entity's transform.
+pub(crate) fn integrate_angular_velocity(
+    mut objects: Query<(&mut Transform, &AngularVelocity)>,
+    time: Res<Time>,
+) {
+    for (mut transform, ang_vel) in &mut objects {
+        let delta = ang_vel.0 * time.delta_secs();
+        let temp = transform.rotation + Quat::from_rotation_z(delta);
+        transform.rotation = temp;
     }
 }