Port pelican to python 3.

Stays compatible with 2.x series, thanks to an unified codebase.

tests/support.py

@@ -1,13 +1,15 @@
+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals, print_function
 __all__ = [
     'get_article',
     'unittest',
 ]
 
-import cStringIO
 import os
 import re
 import subprocess
 import sys
+from six import StringIO
 import logging
 from logging.handlers import BufferingHandler
 
@@ -101,7 +103,7 @@ def mute(returns_output=False):
         def wrapper(*args, **kwargs):
 
             saved_stdout = sys.stdout
-            sys.stdout = cStringIO.StringIO()
+            sys.stdout = StringIO()
 
             try:
                 out = func(*args, **kwargs)