Make CloseButton observer functions private

Now that there's a UI plugin, these systems don't need to be public. So
they won't be.

src/resources.rs

@@ -36,7 +36,7 @@ pub struct UiTheme {
 }
 
 impl FromWorld for UiTheme {
-  fn from_world(world: &mut World) -> Self {
+  fn from_world(_world: &mut World) -> Self {
     Self {
       pane_bg: SLATE_100.into(),
 

src/widgets/machines.rs

@@ -87,7 +87,7 @@ impl RotatingMachine {
           Pickable::default(),
         ))
         .with_children(|cmds| {
-          let button_cmds = cmds.spawn(BigRedButton::bundle("TURN"));
+          let _button_cmds = cmds.spawn(BigRedButton::bundle("TURN"));
           // TODO: Attach on-press observer to the button.
         });
     });

src/widgets/mod.rs

@@ -95,8 +95,11 @@ impl BigRedButton {
   ///
   /// I haven't figure out what will receive the on-press events, so I'm moving
   /// the problem. It will not be the button's job to hook up the event notice.
+  ///
+  /// TODO: Pass in the UiTheme struct 
   fn bundle(text: impl Into<String>) -> impl Bundle {
     (
+      // TODO: Remove `Button`? Add `Button` to the `CloseButton` bundle?
       Button,
       BigRedButton,
       Node {
@@ -182,8 +185,11 @@ pub struct CloseButton(Entity);
 
 impl CloseButton {
   /// Spawn a button that will despawn the top-most node when pressed.
+  ///
+  /// TODO: Pass in the UiTheme struct
   fn bundle(target: Entity) -> impl Bundle {
     (
+      // TODO: Add `Button`? Remove `Button` from the BigRedButton bundle?
       CloseButton(target),
       Node {
         width: Px(20.0),
@@ -208,7 +214,7 @@ impl CloseButton {
     )
   }
 
-  pub fn hover_start(
+  fn hover_start(
     event: Trigger<Pointer<Over>>,
     // Get button background and border colors so we can change them.
     // Filter for *changed* interactions, and only entities with a [`Button`]
@@ -222,7 +228,7 @@ impl CloseButton {
     }
   }
 
-  pub fn hover_stop(
+  fn hover_stop(
     event: Trigger<Pointer<Out>>,
     mut button_colors: Query<(&mut BackgroundColor, &mut BorderColor), With<CloseButton>>,
     ui_theme: Res<UiTheme>,
@@ -233,7 +239,7 @@ impl CloseButton {
     }
   }
 
-  pub fn press_start(
+  fn press_start(
     event: Trigger<Pointer<Pressed>>,
     mut button_colors: Query<(&mut BackgroundColor, &mut BorderColor), With<CloseButton>>,
     ui_theme: Res<UiTheme>,
@@ -244,7 +250,7 @@ impl CloseButton {
     }
   }
 
-  pub fn press_stop(
+  fn press_stop(
     event: Trigger<Pointer<Released>>,
     mut commands: Commands,
     mut button_colors: Query<(&mut BackgroundColor, &mut BorderColor, &CloseButton)>,