Model-metadata

- Nothing changed yet.

- Added constructor for ModelMetadata that accepts an object rather than
a string, better searching for metadata.

- Fixed a bug that raised "object has no attribute '\_\_module\_\_'"
exception when looking for metadata of an instance from an
extension module (22)

- Removed versioneer; use zest.releaser instead

- Changed command line interface to use click (20)

- Query a model by class or name