Derive a default output name from the ELF name.

def default_output_name(self, input_file):
        """ Derive a default output name from the ELF name. """
        irom_segment = self.get_irom_segment()
        if irom_segment is not None:
            irom_offs = irom_segment.addr - ESP8266ROM.IROM_MAP_START
        else:
            irom_offs = 0
        return "%s-0x%05x.bin" % (os.path.splitext(input_file)[0],
                                  irom_offs & ~(ESPLoader.FLASH_SECTOR_SIZE - 1))