Stiffness detection
Stiffness detection for Runge Kutta methods is added, and the methods are given an simpler name.
Other changes to the Runge Kutta base class:
- The stepsize near the end of the integration is different:
- look ahead to prevent too small step sizes
- linear extrapolation if the last step is too small despite it. - the min_step accounts for the distance between C-values
- the scale (weight) is smoothed differently
- a different tolerance validation is used.
Most of these changes originate from the RKSuite code.