New hybrid solver specification

Last week Michal, Walid, Aaron, Veronica and Jan worked on the latest version of the hybrid IVP solver. The result is a much simplified algorithm that Jan feels he understands much better. He also started to update the Scala implementation to fit more closely with the new specification. In the coming week Jan plans to finish the update and start benchmarking the solver to get a better understanding of the current bottlenecks.