Notify of API change in 0.3.2

In 0.3.2, the fix to Issue cpburnz#6 in commit 45829da also changed the API of the spec object to return iterators instead of sets (see cpburnz#6 (comment)). This can break existing code using the library, so should be clearly mentioned

Author: davidfraser

CHANGES.rst

@@ -22,6 +22,7 @@ Change History
 
 - Improved documentation.
 - Issue #6: Fixed matching Windows paths.
+- API change: `spec.match_tree` and `spec.match_files` now return iterators instead of sets
 
 
 0.3.1 (2014-09-17)