switch to pytest test runner for better testing experience

tox.ini

@@ -1,4 +1,4 @@
-# This tests the unified codebase (py27, py33) of Pelican.
+# This tests the unified codebase (py27, py33, p34) of Pelican.
 # depends on some external libraries that aren't released yet.
 
 [tox]
@@ -6,6 +6,9 @@ envlist = py27,py33,py34
 
 [testenv]
 commands =
-    python -m unittest discover
+    py.test tests
 deps =
     -rdev_requirements.txt
+
+[pytest]
+addopts = -vvl