Return grouped, sorted namedtuples in either format: flat, sections.

def get_desc2nts(self, **kws_usr):
        """Return grouped, sorted namedtuples in either format: flat, sections."""
        # desc2nts contains: (sections hdrgo_prt sortobj) or (flat hdrgo_prt sortobj)
        # keys_nts: hdrgo_prt section_prt top_n use_sections
        kws_nts = {k:v for k, v in kws_usr.items() if k in self.keys_nts}
        return self.get_desc2nts_fnc(**kws_nts)