Add new signal: feed_generated

This signal gets emitted before a feed gets written to disk.
Therefore it allows plugins to do arbitrary changes to the feed.

pelican/signals.py

@@ -47,4 +47,5 @@ content_object_init = signal('content_object_init')
 
 # Writers signals
 content_written = signal('content_written')
+feed_generated = signal('feed_generated')
 feed_written = signal('feed_written')

pelican/writers.py

@@ -122,6 +122,7 @@ class Writer(object):
         for i in range(max_items):
             self._add_item_to_the_feed(feed, elements[i])
 
+        signals.feed_generated.send(context, feed=feed)
         if path:
             complete_path = os.path.join(self.output_path, path)
             try: