2012-03-23

    - set_group_type (instead of set_descr())
    - iteration utilities (for -> on option, iter_group -> on 
     OptionDescriptions (group of options)
    - hide and disable for option groups (and subgroups) -> not OK

2012-03-20

    - get() method for recursive attribute access
    - make_path() in a flatten way
    - ro and rw