Flexible penalty lambda and better first guess of p0

Function set_p0 in the fitt.py to give a better first guess
  of parameters p. It uses the median of the inputs.

The penalty lambda is now defined as an object of the module
  and so can be redefined.
Minor version upgrade.
Recording an idea and including verbose

- The optimization now uses a var verbose to define the disp level.
- recording the idea to include weights on the data to be fitted,
    that could resolve the different errors in hybrid dataset.
Do a better first guess of parameters with f.set_p0()
Saves the optimization output status as self.opt_stat
Forgot to actually include the self.opt_stat = op[2] of the previous
commit.
Cleanning duplicate line. I guess I'm quite tired.
Cosmetics on the code.