It's finally here!!
Update 1.6 introduces a completely redone internal custom item system and rearranged API.
The way JSON files are saved and loaded is also redone, so old json files might not work as intended (This affects plugins using this API! See the changelog of CustomCrafting).
The new Custom Item system integrates Oraxen and ItemsAdder into WolfyUtilities and CustomCrafting.

Changelog

• Changed the json library from Gson to Jackson
• JsonConfiguration still uses Gson, but might not be as stable as using Jackson.
• The Language no longer uses the JsonConfiguration
  - LanguageAPI now uses a fallback Language when the specific key isn't found in the active language
  - Languages now cache previous used keys for faster access

• Changed the CustomItem class:
  - it no longer extends Bukkits ItemStack
  - it now extends AbstractItemBuilder that allows for easier creation of Items
  - it is now contains a APIReference variable that can be a VanillaRef, WolfyUtilitiesRef, OraxenRef or ItemsAdderRef.
  - get the ItemStack via:
  getItemStack() - gets the item, linked to the APIReference without amount changes.
  create() - creates a copy of the linked item and uses the custom amount setting.
  
• All the classes are now using custom Jackson Serializer/Deserializer instead of Gson.
• Many other changes and rewritten parts of the API.
• Added many comments to code to explain the methods. (this is unfortunately not yet available)
• Added equals() method to many classes to check for equality.
• Added NamespacedKey to the CustomItem that is added to it when it's saved. That way you can now know when an CustomItem is actually saved by invoking hasNamespacedKey().
• Added back the Custom Equipment Listeners. It now supports equiping from items in the hotbar via right-clicking and full coverage of Inventory clicks like dropping one item, switch items, numberkeys, etc.
• Added new method CustomItem.getReferenceByItemStack() to get a new instance linked to the specific API/Item it's bound to. e.g. If the ItemStack is part of Oraxen this method returns a new CustomItem with the OraxenRef. If the ItemStack has no reference it returns a new CustomItem with the VanillaRef.
• Fixed the check of Player Head textures.
• Fixed that Custom Durability is not completely repairable with Mending
  
• Minor Bug Fixes