Added a MonthYear field, fixed some field required values and fixed

validation functions. Added numeric state abbreviation capability.
So far everything appears to be working good.

model.py

@@ -10,6 +10,7 @@ class Model(object):
                 field = getattr(self, key)
                 if not field.name:
                     setattr(field, 'name', key)
+                setattr(field, 'parent_name', self.__class__.__name__)
 
     def __setattr__(self, key, value):
         if hasattr(self, key) and isinstance(getattr(self, key), Field):