DefaultObjectTransformer to support HashSet

[jwon]

DefaultObjectTransformer supports ArrayList, LinkedList, HashMap, LinkedHashMap, and TreeMap today.

It would be great if we could support the Set classes from java.util as well (e.g. HashSet or TreeSet, etc.)

It should correspond to a Python set object.

Thank you!

[tcalmant]

That seems to be feasible, at least for HashSet.
This could be done for next week.

[jwon]

Thank you so much! 👍

[tcalmant]

I still can't figure out why LinkedHashSet doesn't work... I think I'll stay with HashSet support for now (o allow a release of 0.3.0), with a note in the README.