def save(self, filename, addnormalised=False):
        """Save a frequency list to file, can be loaded later using the load method"""
        f = io.open(filename,'w',encoding='utf-8')
        for line in self.output("\t", addnormalised):
            f.write(line + '\n')
        f.close()
Save a frequency list to file, can be loaded later using the load method