Set metadata in FITS headers.

def set_base_headers(self, hdr):
        """Set metadata in FITS headers."""
        hdr['NUMXVER'] = (__version__, 'Numina package version')
        hdr['NUMRNAM'] = (self.__class__.__name__, 'Numina recipe name')
        hdr['NUMRVER'] = (self.__version__, 'Numina recipe version')
        return hdr