Fix for bug in Enum/choices where Union fields are used

Merge pull request #35 from mpkocher/hotfix-enum

Fix bug for enum case where Union is used in issubclass.

Improve support for simple Enums

Merge pull request #34 from mpkocher/add-enum

Version 3.4.0. Improve support for simple Enums.

Added Support for List/Set

Merge pull request #33 from mpkocher/update-docs-for-list

Bump to 3.3.0. Update docs. Extend List example to include a Set.