Added new PlayerExpChangeEvent and PlayerLevelChangeEvent events. Thanks to feildmaster for the PR.

By: Nathan Adams <dinnerbone@dinnerbone.com>

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

@@ -363,6 +363,18 @@ public abstract class Event implements Serializable {
          * @see org.bukkit.event.player.PlayerChangedWorldEvent
          */
         PLAYER_CHANGED_WORLD(Category.PLAYER, PlayerChangedWorldEvent.class),
+        /**
+         * Called when a players level changes
+         *
+         * @see org.bukkit.event.player.PlayerLevelChangeEvent
+         */
+        PLAYER_LEVEL_CHANGE(Category.PLAYER, PlayerLevelChangeEvent.class),
+        /**
+         * Called when a players experience changes naturally
+         *
+         * @see org.bukkit.event.player.PlayerExpChangeEvent
+         */
+        PLAYER_EXP_CHANGE(Category.PLAYER, PlayerExpChangeEvent.class),
 
         /**
          * BLOCK EVENTS