refactored validators to a class-based concept.  Implemented validate_format
comment update
Updated mongo resource to make use of connection pooling; switched from Connection to MongoClient
Updated requirements to reference pymongo 2.4; defensively initialized connection on first query in order to mock client object for tests, and updated tests
Tagging 1.4.3
The default_message() function now has a @property decorator on all validators
added some changes