Doom fix patch v0.1

This is an unofficial patch that makes a number of fixes on the original Japanese Sega Saturn release of Doom.

What it fixes :

• The nightmare difficulty is available in the main menu and saved in passwords as implemented in PSXDOOM-RE.
• Reinserts the unused inferno sky.
• Visually differentiates nightmare spectres.
• Slightly improves framerate (but the game still very much goes into slideshow territory).
• Stereo CD audio instead of mono.
• Reinserts an unused music (well on Saturn, it is playing on PSX) on the main menu. Automatic exit to the title screen after 30s of inactivity is disabled to allow to hear the full track without having to press buttons regularly. Fixes a bug bug specific to the Saturn version where the exit also happened on returning to the main menu after having spent more than 30s in the options. Exit to title screen is still possible with the classic A+B+C+start.
• Fixes a difference between the volume obtained from the options music volume slider and from track change.
• Corrects pan and pitch for sound effects.
• Increases range and volume for distant sound effects. The sound clipping distance is even longer then on PC vanilla Doom.
• Reinserts an unused fireball explosion sound effect (on Saturn, it is playing on PSX) for :
  • Mancubus projectile explosion.
  • Lost soul explosion.
  • Imp projectile explosion.
  • Cacodemon projectile explosion.
  • Baron of hell projectile explosion.
  • Plasma gun projectile explosion.
  • Arachnotron projectile explosion.
• Can play up to 32 simultaneous sound effects instead of 31.

If you're interested, the minute details of the patch are listed in 2 files :

• The memory map of the original release.
• The fix patch changes.