Various changes.

Added dagger, added arrow types, added new potion image, made bow
properly consume arrows, removed useless badsword initialiser func,
added stackItem func for item stacks, made skeletons ignore the player
when you're dead, made heals that give 0 health show a grey 0, gave the
arrow entity a damage type, boosted the floor count to 15 (might not be
final) and updated the arrow/bow sprites.