Model as dict

as per https://github.com/hyperspy/hyperspy/wiki/HSPEP1%3A-Save-models-in-the-same-hdf5-file-as-the-data

Still lacks user guide entries and tests (any ideas for them are welcome, as none similar are present at the moment)



I see. However, I think that there are advantanges is shallow copying e.g. if the fitting is distributed in the same computer, the map can be updated directly by the sliced model. Beside, one can always make a deepcopy of the sliced model if a deepcopy is needed. What do you think?