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/bolts.rb

@@ -0,0 +1,10 @@
+def create_bolt(item, hash)
+  hash[:projectile_type] = :bolt
+  hash[:weapon_classes]  = [:crossbow]
+  hash[:projectile]      = 27 unless hash.key? :projectile
+  create_ammo item, hash
+end
+
+create_projectile_type :bolt, start_height: 44, end_height: 44, delay: 41, speed: 5, slope: 5, radius: 10
+
+create_bolt :iron_bolts, level_requirement: 1, drop_rate: 0.35