Implementation of the EntityDamage*Events.

A new event EntityDamageByProjectileEvent was created. EntityDamageByProjectileEvent
adds the ability to get the projectile entity (such as an egg) and also set if
the projectile 'bounces'. New interfaces were created to facilitate all kinds
of projectile entities. Changes were made to facilitate the new event, and
enable other events, for plugins and event listeners.

src/main/java/org/bukkit/event/Event.java

@@ -417,6 +417,13 @@ public abstract class Event {
          * @see org.bukkit.event.entity.EntityDamageByEntityEvent
          */
         ENTITY_DAMAGEDBY_ENTITY (Category.LIVING_ENTITY),
+        
+        /**
+         * Called when a LivingEntity is damaged by a projectile Entity
+         *
+         * @see org.bukkit.event.entity.EntityDamageByProjectileEvent
+         */
+        ENTITY_DAMAGEDBY_PROJECTILE (Category.LIVING_ENTITY),
 
         /**
          * Called when a LivingEntity is damaged with no source.