sauvola-ms: fix passing k parameter(s)
Remove sauvola global parameters and use local parameters instead.
API changes
sauvola_ms(const Image<I>& input, unsigned w,
unsigned s,
double k2, double k3, double k4, // <-- New parameters
image2d<mln::util::couple<double,double> >& integral_sum_sum_2);
Fixes #6 (closed)