Deprecate some methods which are likely to require changes in the future

Ref http://mojang.com/2016/08/minecraft-snapshot-16w32a/

By: md_5 <git@md-5.net>

paper-api/src/main/java/org/bukkit/entity/Guardian.java

@@ -6,13 +6,17 @@ public interface Guardian extends Monster {
      * Check if the Guardian is an elder Guardian
      * 
      * @return true if the Guardian is an Elder Guardian, false if not
+     * @deprecated Entity subtypes will be separate entities in a future Minecraft release
      */
+    @Deprecated
     public boolean isElder();
 
     /**
      * Set the Guardian to an elder Guardian or not
      *
      * @param shouldBeElder True if this Guardian should be a elder Guardian, false if not
+     * @deprecated Entity subtypes will be separate entities in a future Minecraft release
      */
+    @Deprecated
     public void setElder(boolean shouldBeElder);
 }