Implement lighting (cells can be illuminated or not), and then the player can only see a short distance around themselves with no light
Allow for mobs and cells to be luminous, and calculate lighting based on line-of-sight of luminous entities
Replace the mob/cell `luminous` attribute with a `luminosity`, which is the number of light sources held, and give items a luminous value.
Add note about updating luminosity
Give mobs an offhand weapon (which currently does nothing), and add a lantern which the player can equip