Support Python 3.3

Closes #23
Make python2.6 the special case

unittest2 is only needed for python2.6, for 2.7 and
onwards we can just use unittest.
Update trove classifiers
Merge branch 'clee704-py33'

* clee704-py33:
  Update trove classifiers
  Make python2.6 the special case
  Support Python 3.3