Create a DisRSTTree instance from a string containing a *.dis parse.

def fromstring(cls, dis_string):
        """Create a DisRSTTree instance from a string containing a *.dis parse."""
        temp = tempfile.NamedTemporaryFile(delete=False)
        temp.write(dis_string)
        temp.close()
        dis_tree = cls(dis_filepath=temp.name)
        os.unlink(temp.name)
        return dis_tree