Added custom world generator API

By: Dinnerbone <dinnerbone@dinnerbone.com>

paper-api/src/main/java/org/bukkit/event/Event.java

@@ -471,6 +471,10 @@ public abstract class Event implements Serializable {
          *
          */
         WORLD_SAVE (Category.WORLD),
+        /**
+         * Called when a World is initializing
+         */
+        WORLD_INIT (Category.WORLD),
         /**
          * Called when a World is loaded
          */

paper-api/src/main/java/org/bukkit/event/world/WorldInitEvent.java

@@ -0,0 +1,9 @@
+package org.bukkit.event.world;
+
+import org.bukkit.World;
+
+public class WorldInitEvent extends WorldEvent {
+    public WorldInitEvent(World world) {
+        super(Type.WORLD_INIT, world);
+    }
+}

paper-api/src/main/java/org/bukkit/event/world/WorldListener.java

@@ -39,6 +39,14 @@ public class WorldListener implements Listener {
         throw new AuthorNagException("onWorldSave has been replaced with a new signature, (WorldSaveEvent)");
     }
 
+    /**
+     * Called when a World is initializing
+     *
+     * @param event Relevant event details
+     */
+    public void onWorldInit(WorldInitEvent event) {
+    }
+
     /**
      * Called when a World is loaded
      *