Add unittest tests that supplement current doctests and go a little bit
further in testing more cases.

git-svn-id: svn+userv://snowball.tartarus.org/snowball/trunk/pystemmer@565 633ccae0-01f4-0310-8c99-d3591da6f01f
tox.ini: Run new unittest-based tests in tox

git-svn-id: svn+userv://snowball.tartarus.org/snowball/trunk/pystemmer@566 633ccae0-01f4-0310-8c99-d3591da6f01f
Make tests/test_pystemmer.py works not use u'' literal syntax on Python
>= 3.0 and < 3.3

git-svn-id: svn+userv://snowball.tartarus.org/snowball/trunk/pystemmer@567 633ccae0-01f4-0310-8c99-d3591da6f01f