v0.6.6

What's Changed

• Add datetime contexts, add datetime validator convenience, update wiki to show other context examples by @timkpaine in #134
• Allow inheritance from callablegeneric type by @timkpaine in #136
• allow CallableModelGenericType to be fully fledged callable model base by @timkpaine in #137

Full Changelog: v0.6.5...v0.6.6