Section attributes

Currently odml.Section() takes name, type, parent and definition.

For me parent does not make sense here. Especially since odml.Property() does not have a parent args.

Another thing: a Section object has a reference attribute, but it can't be defined when creating the Section like it can be done for a Property. In general I think that the reference (if interpreted as reference from where metadata are coming from) is an attribute which should only belong to Properties and not Sections. A Section could contain Properties with metadata coming from different sources.

What do you think?