Inventory: added removeAllListeners()

this isn't strictly necessary because it could be done by removeListeners(...getListeners()), but I think developers will appreciate not needing so much boilerplate code.

src/inventory/BaseInventory.php

@@ -384,6 +384,10 @@ abstract class BaseInventory implements Inventory{
 		}
 	}
 
+	public function removeAllListeners() : void{
+		$this->listeners = [];
+	}
+
 	public function getListeners() : array{
 		return $this->listeners;
 	}

src/inventory/Inventory.php

@@ -164,6 +164,8 @@ interface Inventory{
 	 */
 	public function removeListeners(InventoryListener ...$listeners) : void;
 
+	public function removeAllListeners() : void;
+
 	/**
 	 * @return InventoryListener[]
 	 */