TO DO

* Whole new 1.0 centric test suite.

* Refine documenation.

* General code clean-up.

* Add support for text constructs. It's likely that this
will significantly later the interface. How to avoid
complicating interface access though? Pass around Elemental
elements only? Perhaps a simple subclass?

* Should Person be cut from the hierarchy? In other words
make Author and Contributor a direct descendent of Object?

* Fix inconsistencies in interface. For instance author,
contributor and category have a combined accessor while link
does not implementing a seperate add_link method.

* Writer: better handling of declared namespace?

* Namespace declarations are stored like attributes. Is this
a problem?