Xrf fit

We got a tiny typo, and this one is actually written as
lo_index = np.clip(index - window_p, np.max([xmin, 0]), np.min([xmax, n_background - 1]))
hi_index = np.clip(index + window_p, np.max([xmin, 0]), np.min([xmax, n_background - 1]))

Done!