Removed some usage of np.tile from BernoulliMixture.

- I reshape the ararys instead, which is both more concise, and quite
  possibly much faster.
- Added a plot of the bernoulli mixture example file.
Fixed bug in calculation of log likelihood in bernoulli_mixture.py.
Last fix turned out to be false, so I reverted.
Added support for selecting type in bernoulli_mixture.py.

- This can help avoid memory issues.
Merge branch 'dev-gustav2' of github.com:amitgroup/amitgroup into dev-gustav2

Conflicts:
	amitgroup/stats/bernoulli_mixture.py
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