def set_features(self, filter_type):
        """Calls splitter to split percolator output into target/decoy
        elements.
        Writes two new xml files with features. Currently only psms and
        peptides. Proteins not here, since one cannot do protein inference
        before having merged and remapped multifraction data anyway.
        """
        elements_to_split = {'psm': self.allpsms, 'peptide': self.allpeps}
        self.features = self.splitfunc(elements_to_split, self.ns, filter_type)
Calls splitter to split percolator output into target/decoy
        elements.
        Writes two new xml files with features. Currently only psms and
        peptides. Proteins not here, since one cannot do protein inference
        before having merged and remapped multifraction data anyway.