v0.1.5

• Fixes important bug in v0.1.4 that was causing PETS to break.
• Model.reset() and Model.sample() signature has changed. They no longer receive
  TransitionBatch objects, and they both return a dictionary of strings to tensors
  representing a model state that should be passed to sample() to simulate
  transitions. This dictionary can contain things like previous actions, predicted
  observation, latent states, beliefs, and any other such quantity that the model
  need to maintain to simulate trajectories when using ModelEnv.
• Ensemble class and sub-classes are assumed to operate on 1-D models.