* HDPy/rl.py:
    02.06.2014: ActorCritic.num_step is increased in the beginning of __call__ (not in the end)
    03.06.2014: Removed ActorCritic.init_episode(). Instead use ActorCritic.step_init(epoch) to
                define the behavior during the initial steps.
                ActorCritic._step is changed to have only arguments ActorCritic._step(epoch, reward)
    18.06.2014: reward is written to epoch in rl.ActorCritic
    18.06.2014: rl.ActorCritic.policy is new alias for rl.ActorCritic.child (for convenience and back-compatibility)
* HDPy/hdp.py:
    06.06.2014: - fixed derivative calculation (properly accounting for normalization)
                - ActionGradient properly updated (line search still not working though)
    18.06.2014: - reward is written to epoch in rl.ActorCritic
* HDPy/puppy/puppy.py:
    02.06.2014: removed tumbling detection from PuppyHDP. Tumbling can be
                recorded by a PuPy.TumbleCollector and handled directly
                in the Plant to calculate the appropriate reward.
    18.06.2014: offline_playback() can use a hdf5-file containing all signals that
                were sent during the offline experiment. This is useful for
                e.g. tumbling or reset signaling, or other signal uses.
    18.06.2014: PuppyHDP and OfflinePuppy are created with builder methods,
                such that the base class is variable (e.g. ADHDP or ActionGradient)
* bugfixes