Add changelog entry

CHANGELOG.rst

@@ -30,6 +30,7 @@ Changes:
   `#35 <https://github.com/hynek/attrs/issues/35>`_
 - ``attr.asdict`` can now produce arbitrary mappings instead of Python ``dict``s when provided with a ``dict_factory`` argument.
   `#40 <https://github.com/hynek/attrs/issues/40>`_
+- Multiple performance improvements.
 
 
 ----

src/attr/_make.py

@@ -421,7 +421,8 @@ def fields(cl):
 
 
 def _fast_attrs_iterate(inst):
-    """ Fast internal iteration over the attr descriptors.
+    """
+    Fast internal iteration over the attr descriptors.
 
     Using fields to iterate is slow because it involves deepcopy.
     """