Don't show empty announcement when there's nothing to show.
Souls names are gened from the deceaseded's name
Considerably changes structure of entities

Structs that appear on map (entities) now embed Entity, instead of Entity embedding several other structs.
Fixes death fo mob, and picking items up. By properly removing mob/item from the slice.
Refactors mobs death, moved to mob.die
Properly adds corpse to the item list
Adds the base of the drop system

A getDrops method is used on a Mob type, which returns a list of drops, which right now it just drops a corpse.
Merge branch 'develop' of https://github.com/GGalizzi/rogo into develop