Update CHANGELOG.md

Author: cicirello

CHANGELOG.md

@@ -16,6 +16,13 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   change, as the only thing removed was a package-private abstract class, and the
   change to the SequenceDistanceMeasurer interface was done in such a way that all inherited
   methods have default implementations.
+* Refactored the PermutationDistanceMeasurer, PermutationDistanceMeasurerDouble,
+  NormalizedPermutationDistanceMeasurer, and NormalizedPermutationDistanceMeasurerDouble 
+  interfaces, and all of the classes that implement them, to move default implementations 
+  from an abstract base class into the appropriate subinterfaces in hierarchy. This is a 
+  non-breaking change, as the only thing removed was a package-private abstract class, and the
+  changes to interfaces were done in such a way that all inherited methods have default 
+  implementations.
 
 ### Deprecated