[csharp] Add Skin#removeAttachment.

spine-csharp/src/Skin.cs

@@ -63,6 +63,12 @@ namespace Spine {
 			return attachment;
 		}
 
+		/// <summary> Removes the attachment in the skin for the specified slot index and name, if any.</summary>
+		public void RemoveAttachment (int slotIndex, string name) {
+			if (slotIndex < 0) throw new ArgumentOutOfRangeException("slotIndex", "slotIndex must be >= 0");
+			attachments.Remove(new AttachmentKeyTuple(slotIndex, name));
+		}
+
 		/// <summary>Finds the skin keys for a given slot. The results are added to the passed List(names).</summary>
 		/// <param name="slotIndex">The target slotIndex. To find the slot index, use <see cref="Spine.Skeleton.FindSlotIndex"/> or <see cref="Spine.SkeletonData.FindSlotIndex"/>
 		/// <param name="names">Found skin key names will be added to this list.</param>