Merge branch 'improve-email-validator'
The List validator now passes with objects implementing the list
interface.

refs #18
Now any object implementing the dict interface can be used
as a dict value for the Embedded field.

refs #18
When iterating a model take care of all objects implemeting
the list interface to convert inner models into dicts.

refs #18
Merge branch 'issue-18' into develop

Conflicts:
	tests/unit/fields/test_field.py
	tests/unit/validators/test_validators.py