revised version of#546.

• makest argument required following discussion there. not sure yet that this is the best, but I was almost there already so I just submitted this PR.
• benchmark results in the discussion of that PR that showed that creating a separate callable that skips argument processing had only a small performance advantage, so I decided to leavedynamics as a method.
• leaves code and usage of_rhs and_out unchanged iniosys. The idea is to leave them as fast internal methods and to havedynamics andoutput serve as more user-friendly versions where speed is of less importance.