Now using pytest + tox for testing

- Working with Python 2.6/2.7
- We still have issues with Python 3.x due to 2to3 not being
  executed correctly / tests being run on the old code
More changes to tox/travis configuration
Using threading instead of multiprocessing
Tests up&running with py3k too

* ``setup.py test`` up & running
* ``tox`` up & runing
* So not use py.test directly on the source with py3k, of course!
* Now testing on TravisCI..