tests added, code simplified

- collection.Module added to main api
- loader module method simplified
- more Collection tests, code changed
  raw_items => properties
  raw_items reimplemented,
  raw_values implemented,
  raw method exposed
- sources tests added
collection: bug fix - __len__ method added
__rootfile__ changed into __rootpath__
utils: tests and bug fixes
setup.py: missing supported python version added