Asset structure

@:build(kha.internal.AssetsBuilder.build("image"))
class ImageList {
  var images:Map<String, ImageInstance>;
  public function new() {
  }
}

class ImageInstance {
  var image:kha.Image;
  var load:Void->Void;
  var unload:Void->Void;
}

macro static public function build(type: String): Array<Fields> {
  switch (type) {
    case "image":
      //create map instance here and fill it with ImageInstance objects
  }
}