0.3.0

This includes major changes to the agent interface. The ControlAgent and PredictionAgent traits have been unified into a single trait called Agent with an associated type which distinguishes between control and predictions tasks. The methods associated with choosing actions etc are then defined in Controller for example.

This makes it much easier to build a library of agents that have some, but not all, guarantees about behaviour. This will also make it easier to move into continuous actions space support and better combinability of the various agents (say, when using a predictor inside an actor critic method).

In addition, this push comes with some new agent implementations based on "true online" gradient methods.