Fix two missing monster weightings
Tweak: Thieves now steal one of a stack of items, instead of the entire stack
Fix for thrown items landing in the space in front of the victim rather than the same space as the victim.
Bugfix: Animated attacks (spells and throwing weapons) no longer reset the state to playing if something has already changed it from animation; this resolves an issue where the level-up menu would be inaccessible if the level-up was triggered by a magical attack.
Fix: Don't remove and re-add the player when changing floors; it doesn't hurt for the player to always be referenced by every floor, since only one is ever active at a time, and removing and re-adding risks the possibility of a floor having zero or two references to the player.
Housekeeping
Fix: Make doubly sure that the stairs do not have block_move set; this could've happened if a boulder ended up in the centre of the stair room.
Fix: Unset hitThisTurnMelee each tick in parallel with hitThisTurn; this could've resulted in certain monsters with melee status effects inflicting them when attacking in some other way.
Tweak: Unset poisoner and diseaser when they're no longer relevant (ie when the poison or disease expires); avoids unnecessarily keeping around references of long-dead-and-looted monster corpses.
Tweaked distribution of some monsters, to prevent them from appearing on the first floor. This affects lizards (except the level 0 one), level 2 goblins, and the puck.