`deconstruct` the `default` kwarg as its enum value
Only pass `max_length` for `CharField` backed `EnumField`s
Honor any `choices` explicitly passed in as field options
Use `import_by_path`/`import_string` instead of manually `__import__`ing things
Merge branch 'd1.7'

* d1.7:
  Use `import_by_path`/`import_string` instead of manually `__import__`ing things
  Honor any `choices` explicitly passed in as field options
  Only pass `max_length` for `CharField` backed `EnumField`s
  `deconstruct` the `default` kwarg as its enum value
Bump version to 0.6.0