content: Convert Path.filename to .source_path

Making everything consistent is a bit awkward, since this is a
commonly used attribute, but I've done my best.

Reasons for not consolidating on `filename`:

* It is often used for the "basename" (last component in the path).
  Using `source_path` makes it clear that this attribute can contain
  multiple components.

Reasons for not consolidating on `filepath`:

* It is barely used in the Pelican source, and therefore easy to
  change.
* `path` is more Pythonic.  The only place `filepath` ever show up in
  the documentation for `os`, `os.path`, and `shutil` is in the
  `os.path.relpath` documentation [1].

Reasons for not consolidating on `path`:

* The Page elements have both a source (this attribute) and a
  destination (.save_as).  To avoid confusion for developers not aware
  of this, make it painfully obvious that this attribute is for the
  source.  Explicit is better than implicit ;).

Where I was touching the line, I also updated the string formatting in
StaticGenerator.generate_output to use the forward compatible
'{}'.format() syntax.

[1]: http://docs.python.org/2/library/os.path.html#os.path.relpath

pelican/writers.py

@@ -46,23 +46,23 @@ class Writer(object):
             pubdate=set_date_tzinfo(item.date,
                 self.settings.get('TIMEZONE', None)))
 
-    def write_feed(self, elements, context, filename=None, feed_type='atom'):
+    def write_feed(self, elements, context, path=None, feed_type='atom'):
         """Generate a feed with the list of articles provided
 
-        Return the feed. If no output_path or filename is specified, just
+        Return the feed. If no path or output_path is specified, just
         return the feed object.
 
         :param elements: the articles to put on the feed.
         :param context: the context to get the feed metadata.
-        :param filename: the filename to output.
+        :param path: the path to output.
         :param feed_type: the feed type to use (atom or rss)
         """
         old_locale = locale.setlocale(locale.LC_ALL)
         locale.setlocale(locale.LC_ALL, str('C'))
         try:
-            self.site_url = context.get('SITEURL', get_relative_path(filename))
+            self.site_url = context.get('SITEURL', get_relative_path(path))
             self.feed_domain = context.get('FEED_DOMAIN')
-            self.feed_url = '%s/%s' % (self.feed_domain, filename)
+            self.feed_url = '{}/{}'.format(self.feed_domain, path)
 
             feed = self._create_new_feed(feed_type, context)
 
@@ -72,8 +72,8 @@ class Writer(object):
             for i in range(max_items):
                 self._add_item_to_the_feed(feed, elements[i])
 
-            if filename:
-                complete_path = os.path.join(self.output_path, filename)
+            if path:
+                complete_path = os.path.join(self.output_path, path)
                 try:
                     os.makedirs(os.path.dirname(complete_path))
                 except Exception:
@@ -114,14 +114,14 @@ class Writer(object):
                 output = template.render(localcontext)
             finally:
                 locale.setlocale(locale.LC_ALL, old_locale)
-            filename = os.sep.join((output_path, name))
+            path = os.path.join(output_path, name)
             try:
-                os.makedirs(os.path.dirname(filename))
+                os.makedirs(os.path.dirname(path))
             except Exception:
                 pass
-            with open(filename, 'w', encoding='utf-8') as f:
+            with open(path, 'w', encoding='utf-8') as f:
                 f.write(output)
-            logger.info('writing %s' % filename)
+            logger.info('writing {}'.format(path))
 
         localcontext = context.copy()
         if relative_urls: