Fix TimeStampType for schematics
Add URLType based on dictshield URLField
Add `required_fields` getter property on ModelMeta
Merge remote-tracking branch 'jokull/master' into jokull

* jokull/master:
  Removed a rogue print
  Fixed a bug where default values wouldn't work for embedded models
  Fixed a bug with expanding after flattening into redis hashes.
  Fixed a 'bug' with expand and empty lists/dicts
  Updated setup.py a little bit
  Changed the name of the parameter (inverted it) and added documentation
  Implemented the possibility to skip a field when serializing if the value is None
Merge remote-tracking branch 'jokull/master' into jokull

* jokull/master:
  Changed the behavior of roles regarding subclassing.
  Created a very simple DateType
  Improved roles with regards to subclassing.
Role class which can be handled as a set
Consider role function for equality operator
Refactor filter functions inside Role class

There's no need for the closure in these functions.
Small reordering of methods
Merge branch 'role-set' into jokull

* role-set:
  Small reordering of methods
  Refactor filter functions inside Role class
  Consider role function for equality operator
  Role class which can be handled as a set
Fix TimeStampType convert
Merge branch 'fix-default-update' into jokull

* fix-default-update:
  Fix defaults overriding stored data on update
Fix BooleanType exception to ValidationError
Pass ListType validation errors as dict

Passing as a list was not cleaning up the extra messages from the
ValidationError items. This format is also more standard to parse
as opposed to the tuples format from the sorted list.
Merge remote-tracking branch 'jokull/master' into jokull

* jokull/master:
  Minor cleanup with default types
  Update README.rst
  Update README.rst
Merge remote-tracking branch 'jokull/master' into jokull

* jokull/master:
  Bumb version to 0.2-alpha
  Moved all error messages into type class attribute MESSAGES. A metaclass will merge all MESSAGES dicts. Pass in `messages` dict at instance level to override error messages per instance.
  Bumped the version to 0.1-alpha
  Made EmailType raise StopValidation on invalid emails.

Conflicts:
	schematics/types/base.py
Allow fields to be appended to existing Model
Merge branch 'append-fields' into jokull

* append-fields:
  Allow fields to be appended to existing Model
Catch TypeError on number conversion
Merge remote-tracking branch 'jokull/master' into jokull

* jokull/master:
  Fixed a crash bug when flattening models with roles and serializables.