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/ammo.rb

@@ -0,0 +1,34 @@
+AMMO = {}
+
+def create_ammo(item_matcher, properties, &block)
+  items = find_entities :item, item_matcher, -1
+  fail "Unable to find ammo matching #{item_matcher}" unless items.size > 0
+
+  projectile_type = properties[:projectile_type]
+  fail "Unable to find projectile type #{projectile_type}" unless PROJECTILE_TYPES.key? projectile_type
+
+  properties[:projectile_type] = PROJECTILE_TYPES[projectile_type]
+
+  items.each do |item_id|
+    AMMO[item_id] = Ammo.new(item_id, properties)
+    AMMO[item_id].instance_eval &block if block_given?
+  end
+end
+
+private
+
+class Ammo
+  attr_reader :item, :weapon_classes, :projectile, :projectile_type, :level_requirement, :drop_rate, :graphic
+
+  include Combat::BonusContainer
+
+  def initialize(item, weapon_classes:, projectile:, projectile_type:, level_requirement:, drop_rate:, graphic: nil)
+    @item              = item
+    @weapon_classes    = weapon_classes
+    @projectile        = projectile
+    @projectile_type   = projectile_type
+    @level_requirement = level_requirement
+    @drop_rate         = drop_rate
+    @graphic           = graphic
+  end
+end