examples: wrong description fixed
collection: tests for __str__, __repr__, __unicode__ added
utils: private_attribute_name - function to correctly construct private attribute name added
collection changes: private / shared data mechanism added

- all the collection objects may now receive not only data, but also
  private stuff that is convinient to share with properties.
- tests for the case where adopted
- no public api changes introduced
new release version updates (ver 3.3.4)