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.
Now the legacy drill.map.type and drill.report.filename are specified in this
way.
The BaseOutput class now inherits from Optionable.
Suboptions are just Optionable classes.
Also: added traceback print when an error is reported and we are in debug mode.
Salvador E. Tropea