Tool: cleanup durability handling, closes #379

long overdue... this isn't quite as extensible as the original api3/blocks system was, but this is primarily intended to replace Item->useOn(). If plugins want to use it it can be extended later on.

src/pocketmine/item/Item.php

@@ -715,15 +715,6 @@ class Item implements ItemIds, \JsonSerializable{
 		return 0;
 	}
 
-	/**
-	 * @param Entity|Block $object
-	 *
-	 * @return bool
-	 */
-	public function useOn($object){
-		return false;
-	}
-
 	/**
 	 * Returns what type of block-breaking tool this is. Blocks requiring the same tool type as the item will break
 	 * faster (except for blocks requiring no tool, which break at the same speed regardless of the tool used)
@@ -814,6 +805,28 @@ class Item implements ItemIds, \JsonSerializable{
 		return false;
 	}
 
+	/**
+	 * Called when this item is used to destroy a block. Usually used to update durability.
+	 *
+	 * @param Block $block
+	 *
+	 * @return bool
+	 */
+	public function onDestroyBlock(Block $block) : bool{
+		return false;
+	}
+
+	/**
+	 * Called when this item is used to attack an entity. Usually used to update durability.
+	 *
+	 * @param Entity $victim
+	 *
+	 * @return bool
+	 */
+	public function onAttackEntity(Entity $victim) : bool{
+		return false;
+	}
+
 	/**
 	 * Returns the number of ticks a player must wait before activating this item again.
 	 *