Add Pool for tracking current and max stat values.

src/core.rs

@@ -434,6 +434,12 @@ impl From<&dyn PointLike> for (i32, i32) {
 #[reflect(Component)]
 pub struct Player;
 
+#[derive(Clone, Copy, Debug)]
+pub struct Pool<T> {
+    pub value: T,
+    pub max: T,
+}
+
 fn copy_coordinates_to_transform(
     config: Res<CoreConfig>,
     mut query: Query<(&Coordinates, &mut Transform)>,