Cache content to speed up reading. Fixes #224.

Cache read content so that it doesn't have to be read next time if its
source has not been modified.

pelican/contents.py

@@ -325,6 +325,13 @@ class Content(object):
             os.path.abspath(self.settings['PATH']))
         )
 
+    def __eq__(self, other):
+        """Compare with metadata and content of other Content object"""
+        return other and self.metadata == other.metadata and self.content == other.content
+
+    # keep basic hashing functionality for caching to work
+    __hash__ = object.__hash__
+
 
 class Page(Content):
     mandatory_properties = ('title',)