Contique

Highlights of this relase:
- set central differences (3-point mode) as default jacobian approximation `jacmode=3`
- automatic `jaceps` based on machine epsilon if `jaceps=None`
- complete docstring documentation for all functions and classes

If the control component changes during a cycle but the final control component is within a valid range of overshoot, then no re-cycle of a step is performed. This should prevent Errors due to "cyclic permutations" of the control component until max. numbers of cycles is reached:

- Cycle 1, Control -1 to +2
- Cycle 2, Control +2 to -4
- Cycle 3, Control -4 to -7
- Cycle 4, Control -7 to -1
- ...

- adapt README for new print statements
- raise to version 0.1.5

- smaller information of step/cycle/converged
- initial `res` object now contains `jac`
- moved all print statements from solver.py to printinfo.py
- calculate final `jac` in newtonrhapson.py
- added 2 new examples