Prepare for 0.0.2.
Add map.
Update signature
Add flatMap, make functions serializable.
Add filter.
Add groupBy.  Also tightens up some Cascading validation.
Add reduce.  Needs a unit test for reduce operation.
Add missing class with test.
Add count.
Method to convert KeyValue to List<String>, for ease of writing to file.
Use immutable list.
Tidy up.
Add group method.
Release 0.0.2.