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/attributes.rb

@@ -1,6 +1,6 @@
 ##
-# The delay a <i>Mob</i> must wait before attacking again.
-declare_attribute(:attack_delay, 0)
+# The number of ticks since a <i>Mob<i>s last attack.
+declare_attribute(:attack_timer, 100)
 
 ##
 # A flag indicating whether this <i>Mob</i> is currently in combat.
@@ -22,6 +22,10 @@ declare_attribute(:combat_style, 0, :persistent)
 # A flag indicating whether the special bar is flagged for the next attack.
 declare_attribute(:using_special, false, :persistent)
 
+##
+# A flag indicating whether auto retaliation is enabled.
+declare_attribute(:auto_retaliate, true, :persistent)
+
 ##
 # An integer between 0 and 100 indicating the amount of special energy a <i>Player</i> has.
 declare_attribute(:special_energy, 100, :persistent)