Steenzout-serialization-json

- fixed serialization of objects that may have attributes of type `datetime.date`: 3
- renamed `version` module to `metadata`
- documentation
- use [steenzout.sphinx](https://github.com/steenzout/python-sphinx/) to generate documentation
- travis-ci
- change which directories to cache on [travis-ci](https://travis-ci.org/)

- add ability to handle classes with properties : 1
- hide object attributes that start with `_` : 2

- added `serialize()` and `deserialize()`
- added serialization/deserialization support for:
- `object`
- `datetime.datetime`