Various changes.

Added starting 'armour', changed how player defence is calculated (to
reduce OP/UPness), added some flavour messages to discovering things
about items (i.e. sharpness), added a healing potion, the necklace image
is picked from 3 possible images, the sword image is picked from 2
possible images, changed the entity move function to use a direction
(cleaner), changed the starting chest to contain a feeding necklace and
3 potions (may change), changed range of skeleton spawn (might crash
game now if player spawns right at edge) and some other things.