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/entity/EntityDamageByProjectileEvent.java

@@ -0,0 +1,35 @@
+package org.bukkit.event.entity;
+
+import java.util.Random;
+
+import org.bukkit.entity.Entity;
+
+public class EntityDamageByProjectileEvent extends EntityDamageByEntityEvent {
+
+    private Entity projectile;
+    private boolean bounce;
+
+    public EntityDamageByProjectileEvent(Entity damager, Entity damagee, Entity projectile, DamageCause cause, int damage) {
+        super(damager, damagee, cause, damage);
+        this.projectile = projectile;
+        Random random = new Random();
+        this.bounce = random.nextBoolean();
+    }
+
+    /**
+     * The projectile used to cause the event
+     * @return the projectile
+     */
+    public Entity getProjectile() {
+        return projectile;
+    }
+
+    public void setBounce(boolean bounce){
+        this.bounce = bounce;
+    }
+
+    public boolean getBounce(){
+        return bounce;
+    }
+
+}