-debug_briks = add sub-briks with Ed (error functional), Ed0 (orig.
                  error), number of steps to convergence and I0 (modeled B0
                  volume).
                  [May, 2017] This also now calculates two goodness-of-fit
                  measures and outputs a new PREFIX_CHI* dset that has two
                  briks:
                     brik [0]: chi^2_p,
                     brik [1]: chi^2_c.
                  These values are essentially calculated according to
                  Papadakis et al. (2003, JMRI), Eqs. 4 and 3,
                  respectively (in chi^2_c, the sigma value is the
                  variance of measured DWIs *per voxel*). Note for both
                  chi* values, only DWI signal values are used in the
                  calculation (i.e., where b>THR; by default,
                  THR=0.01, which can be changed using '-bmax_ref ...').
                  In general, chi^2_p values seem to be <<1, consistent
                  with Papadakis et al.'s Fig. 4; the chi^2_c values are
                  are also pretty consistent with the same fig and seem to
                  be best viewed with the upper limit being roughly =Ndwi
                  or =Ndwi-7 (with the latter being the given degrees
                  of freedom value by Papadakis et al.)