Dispatching for Nystrom #147
Description
Currently the factory function TimeStepper takes a stage_type argument and such and produces the proper subclass.
Adding DIRK/explicit steppers for Nyström will create a similar situation. Do we want NystromTimeStepper as a factory function with stage_type that could be derivative, dirk or explicit and then dispatch to the right subclass? This seems like it's the most parallel to what we've got.
Eventually, we could have TimeStepper -> RKTimeStepper and then a TimeStepper that dispatches over both first and second order equations...
Thoughts?