Can't use @propertys on Entities

[six8]

Python's __setattr__ has precedence over descriptors like @property. If you do, you'll get:

  File "/python2.7/site-packages/springfield/entity.py", line 203, in __setattr__
    raise AttributeError('Field %r not defined.' % name)

Entity needs to be modified to allow properties:

if name in self.__fields__ or isinstance(getattr(self.__class__, name, None), property):
    object.__setattr__(self, name, value)
else:
    raise AttributeError('Field %r not defined.' % name)

As a workaround, the following can be added to any Entity to support properties:

def __setattr__(self, name, value):
        if name not in self.__fields__ and isinstance(getattr(self.__class__, name, None), property):
            object.__setattr__(self, name, value)
        else:
            super(EntityName, self).__setattr__(name, value)