RF: add helpers function _wls_iter which process the water elimination model at the voxel level
RF: add helpers function _wls_iter which process the water elimination model at the voxel level

FrancoisRheaultUS/dipy,villalonreina/dipy,FrancoisRheaultUS/dipy,nilgoyyou/dipy,matthieudumont/dipy,nilgoyyou/dipy,matthieudumont/dipy,villalonreina/dipy