Do not depend on flask-views package (#121)

The package only uses [1] which just sets ``self.args`` and ``self.kwargs`` that
are not used anywhere.

[1]: https://github.com/brocaar/flask-views/blob/master/flask_views/base.py#L5-L36

Merge pull request #114 from closeio/extensible-resource-serialize-fi…

…elds

Extensible resource field serialization