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

def prt_details(self, prt=sys.stdout):
        """Print summary of codes and groups that can be inputs to get_evcodes."""
        prt.write('EVIDENCE CODES:\n')
        for grp, code2nt in self.grp2code2nt.items():
            prt.write('    {GROUP}:\n'.format(GROUP=grp))
            for code, ntd in code2nt.items():
                prt.write('        {CODE:>3} {NAME}\n'.format(CODE=code, NAME=ntd.name))