The Model class now has a deserialize classmethod
and serialize method supporting field names mapping.

refs #16
Little refactor in the serialize/deserialize code

refs #16
The List validator now accepts None as a valid value
Added a List field
Merge branch 'improve-email-validator' into develop

Conflicts:
	CHANGES.rst
Merge branch 'issue-18' into develop

Conflicts:
	tests/unit/fields/test_field.py
	tests/unit/validators/test_validators.py
Updated serialization and deserialization to support
objects with the dict and list interfaces.

refs #18
refs #16
Fixed CHANGES from last merge
Merge branch 'master' into develop
Merge branch 'master' into develop

Conflicts:
	CHANGES.rst
Fix support for deserializing optional parameters
Merge pull request #19 from bodylabs/fix_deserialize

Fix support for deserializing optional parameters
Refactor. refs #16

 * Renamed serialize and deserialize Model methods to encode and decode.
 * Extracted serialization/deserialization logic to fields and encoders/decoders.
Fixed markup
Added datetime validator
Added datetime decoder
Added datetime encoder
Extracted the nullable decorator to a helpers module
Merge branch 'master' into develop

Conflicts:
	CHANGES.rst
	booby/fields.py
	booby/models.py
Merge branch 'develop'