message: custom_config example ui
diff: use zoon::*;
  #[static_ref]
  -fn counter() -> &'static Mutable<i32> {
  - Mutable::new(0)
  +fn favorite_languages() -> &'static Mutable<String> {
  + Mutable::new("Loading...".to_owned())
  }
  fn root() -> impl Element {
  - Text::new("Custom Config")
  + Column::new()
  + .s(Align::center())
  + .s(Spacing::new(60))
  + .s(Font::new().size(20))
  + .item(
  + El::with_tag(Tag::H1)
  + .s(Font::new().size(30))
  + .child("Variables loaded from MoonZoonCustom.toml")
  + )
  + .item(
  + Row::new()
  + .s(Spacing::new(20))
  + .multiline()
  + .item(El::new().s(Font::new().no_wrap()).child("my_api / MY_API:"))
  + .item(El::new().s(Font::new().weight(FontWeight::Bold)).child(env!("MY_API")))
  + .item(El::new().s(Font::new().italic()).child("(included at compile time)"))
  + )
  + .item(
  + Row::new()
  + .s(Spacing::new(20))
  + .multiline()
  + .item(El::new().s(Font::new().no_wrap()).child("favorite_languages / FAVORITE_LANGUAGES:"))
  + .item(El::new().s(Font::new().weight(FontWeight::Bold)).child_signal(favorite_languages().signal_cloned()))
  + .item(El::new().s(Font::new().italic()).child("(loaded at runtime)"))
  + )
  }
  #[wasm_bindgen(start)]
  