Updated CHANGELOG to mention custom arg match and describer features

CHANGELOG.txt

@@ -1,4 +1,6 @@
 unreleased changes
+* [NEW] Detailed descriptions for custom argument matchers using IDescribeNonMatches interface.
+* [NEW] Custom argument matchers (Arg.Matches syntax).
 * [FIX] Race condition between checking received calls and building the exception could cause nonsensical exception messages like "Expected 5, actually received 5" when called concurrently. (#64)
 
 1.3.0 (Nov 2011)