Add the beginning of item entities

Add a new Item raw type and entity type, with preliminary, basic support
for food. There's a really frustrating toml-rs bug that prevents writing
these nicely as toml right now, so I also added support for mixing JSON
and TOML in a single config dir

src/messages.toml

@@ -9,3 +9,6 @@ killed = [
     "The {{creature.name}} kicks it.",
     "The {{creature.name}} beefs it."
     ]
+
+[defaults.item]
+eat = "You eat the {{item.name}}"