Fix pinball and add example on using Ipython parallel

This example shows how to use the special `TrajectoryRecorder` decorator for saving trajectories. Furthermore, it uses [IPython parallel](http://ipython.org/ipython-doc/rel-1.1.0/parallel/index.html) to compute the performance of many agents in parallel.
    
It can be used over a guerilla SSH cluster over the computers in your lab, or more cleanly on an MPI, PBS or AWS cluster.
    
For local parallel computation, execute in a separate tab:
`$ ipcluster start -n 4`
    
followed by
`$ python learn-flat-policy.py -a 100 -n 100 pinball_simple_single.cfg`