Updates for spectroscopic data reductions

Updates to add iterative reweighting least squares to make the fitting m..ore robust to outliers. Added a gaussian process fit for the sensitivity function. Added fitting the full cross-correlation option to interidentify.
change to use spectools.smooth_image instead.  Although looking at that now, it does a gaussian smooth, but maybe just move the smoothing task from pyspectrograph to spectools for a boxcar smoothing