Added ability to add caption to ag.plot.images.
Improved blurring and added a new zeropad function.

- Blurring can now take non-integer sigmas.
- Added a zeropad_to_shape function.
- Removed some temporary outputs from plot/images.py.
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.