Unify examples structure (#1118)

* Animations, CameraAndViewport, CollisionDetection and Components unified

* Added descriptions to effects

* Rename input games

* Unify input stories

* Add info to parallax section

* Added descriptions to the rendering examples

* Add descriptions to the sprites directory

* Fix utils and rendering section

* Add descriptions to the widgets section

* Delete directory that rebase brought back

* Unify game names

* Added some styleguide docs for examples

* Fix analyze issues

* All files should have _example as suffix

* Made the FollowComponentExample a bit easier to understand

* Change priority of ember

examples/lib/stories/sprites/sprite_group_example.dart

@@ -0,0 +1,65 @@
+import 'package:flame/components.dart';
+import 'package:flame/game.dart';
+
+enum ButtonState { unpressed, pressed }
+
+class SpriteGroupExample extends FlameGame with HasTappables {
+  static const String description = '''
+    In this example we show how a `SpriteGroupComponent` can be used to create
+    a button which displays different sprites depending on whether it is pressed
+    or not.
+  ''';
+
+  @override
+  Future<void> onLoad() async {
+    await super.onLoad();
+    add(
+      ButtonComponent()
+        ..position = size / 2
+        ..size = Vector2(200, 50)
+        ..anchor = Anchor.center,
+    );
+  }
+}
+
+class ButtonComponent extends SpriteGroupComponent<ButtonState>
+    with HasGameRef<SpriteGroupExample>, Tappable {
+  @override
+  Future<void> onLoad() async {
+    await super.onLoad();
+    final pressedSprite = await gameRef.loadSprite(
+      'buttons.png',
+      srcPosition: Vector2(0, 20),
+      srcSize: Vector2(60, 20),
+    );
+    final unpressedSprite = await gameRef.loadSprite(
+      'buttons.png',
+      srcSize: Vector2(60, 20),
+    );
+
+    sprites = {
+      ButtonState.pressed: pressedSprite,
+      ButtonState.unpressed: unpressedSprite,
+    };
+
+    current = ButtonState.unpressed;
+  }
+
+  @override
+  bool onTapDown(_) {
+    current = ButtonState.pressed;
+    return true;
+  }
+
+  @override
+  bool onTapUp(_) {
+    current = ButtonState.unpressed;
+    return true;
+  }
+
+  @override
+  bool onTapCancel() {
+    current = ButtonState.unpressed;
+    return true;
+  }
+}