contents: Add URLWrapper.__repr__

This makes it easier to troubleshoot collections of URLWrappers,
because printing the collection will give you something you can
actually read ;).

pelican/urlwrappers.py

@@ -41,6 +41,9 @@ class URLWrapper(object):
     def __str__(self):
         return self.name
 
+    def __repr__(self):
+        return '<{} {}>'.format(type(self).__name__, str(self))
+
     def _from_settings(self, key, get_page_name=False):
         """Returns URL information as defined in settings.