Remove the 'NSFW' tagged (and commented out by default) parts in creature defs.

Part of #6.
Remove BODY:NEUTRAL. All it defines are tongues, which are defined by TONGUE and FORKED_TONGUE in the base raws.

Plus it has an ID that is inconsistent with the base game.
Address the explosion of nightmare populations detailed in #8.

Unfortunately, this has the side effect of disabling underground nightmare spawns. Even if nightmares are underground-only they quickly become the most populous thing on the planet.

It's rather unfortunate.
Weaken the succubus saliva syndrome.

Previously, it basically caused certain death in any small creatures afflicted by it. Like dwarves, humans, and elves.

This fixes #8, though the syndrome probably needs revisiting at a later date, as it is still rather powerful.