Initial pass of removing Python 2 support

This commit removes Six as a dependency for Pelican, replacing the
relevant aliases with the proper Python 3 imports. It also removes
references to Python 2 logic that did not require Six.

pelican/writers.py

@@ -1,24 +1,18 @@
 # -*- coding: utf-8 -*-
-from __future__ import print_function, unicode_literals, with_statement
 
 import logging
 import os
+from urllib.parse import urljoin
 
 from feedgenerator import Atom1Feed, Rss201rev2Feed, get_tag_uri
 
 from jinja2 import Markup
 
-import six
-from six.moves.urllib.parse import urljoin
-
 from pelican import signals
 from pelican.paginator import Paginator
 from pelican.utils import (get_relative_path, is_selected_for_writing,
                            path_to_url, sanitised_join, set_date_tzinfo)
 
-if not six.PY3:
-    from codecs import open
-
 logger = logging.getLogger(__name__)
 
 
@@ -165,8 +159,7 @@ class Writer(object):
             except Exception:
                 pass
 
-            encoding = 'utf-8' if six.PY3 else None
-            with self._open_w(complete_path, encoding, override_output) as fp:
+            with self._open_w(complete_path, 'utf-8', override_output) as fp:
                 feed.write(fp, 'utf-8')
                 logger.info('Writing %s', complete_path)