Add ranged combat support

* Clean up the CombatAction and Attack code to make it easier to use for
  range.

* Add collision detection to the distance checks before attacking in the
  CombatAction.

* Create a Ruby DSL for defining projectile types and fix the
  ProjectileUpdateOperation so it uses the correct position offset.

* Fix the packet structure of the HintIconMessageEncoder.

data/plugins/combat/equipment.rb

@@ -6,7 +6,7 @@ def create_equipment(item, &block)
   equipment = Equipment.new
   equipment.instance_eval block
 
-  find_entities :item, item do |equipment_item|
+  find_entities :item, item do |_equipment_item|
     EQUIPMENT[id] = equipment
   end
 end
@@ -15,4 +15,4 @@ private
 
 class Equipment
   include Combat::BonusContainer
-end
+end