Can pickup item from ground. Nothing to store it in yet.
Mobs convert to item(corpse) when they die.
Adds effect to item, able to use them. (Not yet handled by input)
Potions have their own potency.
Player can open usable inventory, and use an item.
Don't use unusable items.
Only list usable items when press 'u'
Log the use of items.
Merge branch 'feature/inventory' into develop