load_example('faces') returns a numpy array again.
Merge branch 'master' of github.com:amitgroup/amitgroup
DOC: Better description of mnist.
Merge branch 'master' of github.com:amitgroup/amitgroup into dev-gustav2
Added BinaryDescriptor and PartsDescriptor.

- Also added Saveable, which is a key-value coding interface.
- Added an example of using PartsDescriptor on MNIST.
Merge branch 'dev-gustav2' of github.com:amitgroup/amitgroup into dev-gustav2