'Formats a field\'s value. No-op by default - field classes that
modify how the value of existing object keys should be presented should
override this and apply the appropriate formatting.
:param value: The value to format
:exception MarshallingException: In case of formatting problem
Ex::
class TitleCase(Raw):
def format(self, value):
return unicode(value).title()'

def format(self, value):

    return value
