BF: the multi_voxel_model decorator couldn't be pickled and therefore used with multi processing. The solution was to decorate only the fit method and not the entire model.
Updated csdeconv, dsi and gqi to work with the new multi_voxel_fit decorator
Merge pull request #1 from Garyfallidis/parallel_peaks_extraction

Made CSD, DSI, GQI and SDT pickable so that they can be parallelized