Now the GS members contains the absolute path and various useful parts
of the name are computed and stored in GS to avoid computing them in
each output.
Now the options are just an attribute of the outputs.
It means we have a set of classes for the options.
All the output content is parsed by the classes, including the Layers.
Now the layers support a simple string (with interesting shortcuts), a list of
strings or the original list of dicts.
Salvador E. Tropea