Add DecimalField and UUIDField.
Update Model __metaclass__ to add fields from parent classes to allow model inheritance.
Serialize UUIDField to the UUID's hex value.
Allow for a default value to be set on fields.
Add basic validation.
Slight PEP8 cleanup.
Merge remote-tracking branch 'dmpayton/v0.6.0-devel'

Conflicts:
	micromodels/fields.py
	micromodels/models.py
	tests.py