feat(gs/xanthous): Creatures use their weapons to attack

If a creature has a weapon wielded, then they now use that weapon to
attack the player *instead of* their natural attacks. This uses a new
`creatureAttackMessage` field on the Item raw for the message to use.

Change-Id: I73614f33dbf88dd4c68081f15710fa27b7b21ba2

users/grfn/xanthous/src/Xanthous/messages.yaml

@@ -80,7 +80,9 @@ combat:
     generic:
       - You hit the {{creature.creatureType.name}}.
       - You attack the {{creature.creatureType.name}}.
-  creatureAttack: The {{creature.creatureType.name}} {{attackDescription}}
+  creatureAttack:
+    natural: The {{creature.creatureType.name}} {{attackDescription}}.
+    genericWeapon: The {{creature.creatureType.name}} attacks you with its {{item.itemType.name}}.
   killed:
     - You kill the {{creature.creatureType.name}}!
     - You've killed the {{creature.creatureType.name}}!