Merge all psms and peptides

def set_features(self):
        """"Merge all psms and peptides"""
        allpsms_str = readers.generate_psms_multiple_fractions_strings(
            self.mergefiles, self.ns)
        allpeps = preparation.merge_peptides(self.mergefiles, self.ns)
        self.features = {'psm': allpsms_str, 'peptide': allpeps}