Added AnimBatcher, Util.new_object(); tidy.

Util: added new_object().

AssetLoader: added __id to table assets; tidy.

Animator: added AnimBatcher; tidy.

AudioManager: use __id instead of data for indexing; tidy.

Core:
    switched moving_square to test AnimBatcher;
    disable State.debug_mode after init.
AssetLoader: default filenames; made font descriptor defaultable with opt.

AssetLoader:
    default filenames based on asset kind;
    added desc.path and .ext;
    made font descriptor defaultable with opt instead of by path.