Pass around iLiving references instead of target indices in most combat contexts (and some non-combat)

- Fixes PC melee attacks using webs from the wrong PC
- Support for PC-on-PC attacks is in place, though these code paths are currently not entered; could be used for charmed PCs, for example
- In many cases, status effects that don't affect monsters are now supported for them (but still don't affect them... yet)
- The "special" damage from assassination is now handled differently; support for it is no longer hard-coded into damage_monst(), and the message display for it is handled externally from damage_monst(). Also, it's no longer used for any kind of magic weapons.
- Select target special node has changed its way of selecting a specific monster/PC as the target
- Fix monster-on-monster attacks applying poison on all three attacks instead of just the first

rsrc/strings/specials-text-affect.txt

@@ -9,8 +9,8 @@ Unused
 0 - only living, 1 - any, 2 - all, 3 - dead, 4 - inv. space
 Special if Cancel button pressed
 Unused
-0 - player choice, 1 - random, 11..16 - specific, 100+ monster
-Unused
+0 - player choice, 1 - random, 2 - specific
+0..6 - PC, 100+ - monster (if above = 2)
 Unused
 Special to Jump To
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