Datatyping

- Better exception messages with `reprlib.repr`
- External documentation (http://datatyping.rtfd.io)
- Checks that types are actually the same or a subclass instead of just of the
same abstract type Sequence/Mapping

- Replaced "contracts" with customtype
- Works with all `collections.abc.Mapping` instead of just dicts.
- `validate` throws ValueError instead of undocumented AssertionError.
- New description: "Pythonic type checking"
- First PyPI release!

- Added support for tuples
- Fixed bug with str (not considered sequence anymore)
- Reasonble versioning scheme :p

- Added printer

- Added contracts

- Initial release