Print summary of codes and groups that can be inputs to get_evcodes.

def prt_summary_code(self, prt=sys.stdout):
        """Print summary of codes and groups that can be inputs to get_evcodes."""
        prt.write('EVIDENCE GROUP AND CODES:\n')
        for grp, c2nt in self.grp2code2nt.items():
            prt.write('    {GRP:19}: {CODES}\n'.format(GRP=grp, CODES=' '.join(c2nt.keys())))