Open given TI-TXT file and add its contents. Set `overwrite` to
        ``True`` to allow already added data to be overwritten.

def add_ti_txt_file(self, filename, overwrite=False):
        """Open given TI-TXT file and add its contents. Set `overwrite` to
        ``True`` to allow already added data to be overwritten.

        """

        with open(filename, 'r') as fin:
            self.add_ti_txt(fin.read(), overwrite)