Extensisq

Runge Kutta Nyström methods added.

Added sensitivity analysis and Me4 method.
Updated and extended documentation (examples).

simplifications
step size control settings modified for some methods
revert to original weight vector in SSV2stab

Include two methods for specific problems:
- CFMR7osc for oscillatory problems
- SSV2stab: for large mildly stiff problems

update and enable stepsize control for standard RK methods.

Add second order stepsize control for Runge Kutta methods. (Not enabled by default yet)
Fix bugs stiffness detection.