Restore

This implements non-linear least-squares fitting of the DTI model, including the RESTORE algorithm, described in Chang et al. (2005):     Chang, L-C, Jones, DK and Pierpaoli, C (2005). RESTORE: robust estimation of tensors by outlier rejection. MRM, 53: 1088-95.

Testing of this is not very comprehensive, because producing testable outliers with noiseless data is kinda hard. Tips and comments on that would be much appreciated