emulators/mame: update to 0.257
- Update to 0.257 (https://www.mamedev.org/?p=527)
- Add a hopefully more meaningful description for option NLS
- Fix description on option QTDEBUGGER, it is built as part of MAME, not installed separately as might be implied
- Clean up pkg-message.in and hopefully clarify the mess with MAME configuration data.
PR: 272786