add test framework

- add the ability to run tests from the top level directory via
  'python setup.py test'
- translate runtest.py into a test that runs under this framework
- add a __main__ section to Tests/runtest.py and change its indent to 4
  spaces; make no other changes to this script

setup.py

@@ -48,4 +48,5 @@ using the tutorial http://propka.ki.ku.dk/~luca/wiki/index.php/PROPKA_3.1_Tutori
             ],
         },
       zip_safe=True,
+      test_suite="Tests",
 )