Function sg_smooth

! \brief savitzky golay smoothing. * * This method means fitting a polynome of degree 'deg' to a sliding window * of width 2w+1 throughout the data. The needed coefficients are * generated dynamically by doing a least squares fit on a "symmetric" unit * vector of size 2w+1, e.g. for w=2 b=(0,0,1,0,0). evaluating the polynome * yields the sg-coefficients. at the border non symmectric vector