Implemented Workshop Item Subscription

Added subscribing to items as well as the UGC interfaces
GetNumSubscribedItems and GetSubscribedItems. Edited SteamUGC Method
GetSubscribedItems to accept array instead of a ptr to allow c# calling

Facepunch.Steamworks/Interfaces/Workshop.Item.cs

@@ -63,6 +63,19 @@ public void Download( bool highPriority = true )
                 workshop.OnItemInstalled += OnItemInstalled;
             }
 
+            public void Subscribe()
+            {
+                workshop.ugc.SubscribeItem(Id);
+                SubscriptionCount++;
+            }
+
+            public void UnSubscribe()
+            {
+                workshop.ugc.UnsubscribeItem(Id);
+                SubscriptionCount--;
+            }
+
+
             private void OnFileDownloaded( ulong fileid, Callbacks.Result result )
             {
                 if ( fileid != Id ) return;

Facepunch.Steamworks/Interfaces/Workshop.cs

@@ -123,6 +123,37 @@ public Item GetItem( ulong itemid )
             return new Item( itemid, this );
         }
 
+        /// <summary>
+        /// The amount of item's the user is subscribed to for this App
+        /// </summary>
+        public uint GetAmountSubsribed()
+        {
+            return ugc.GetNumSubscribedItems();
+        }
+        /// <summary>
+        /// Creates a list of all item's that the user is currently subscribed
+        /// to for this App. This does not query titles or descriptions but
+        /// allows you to get the directories, state and ID of any subscribed Item.
+        /// This is mostly useful for getting all subscribed items install location.
+        /// </summary>
+        public Item[] GetSubscribedItems(uint amount)
+        {
+            Item[] items;
+            PublishedFileId_t[] vecSubscribedItems = new PublishedFileId_t[amount];
+            uint subAmount = ugc.GetSubscribedItems(vecSubscribedItems, amount);
+
+            if (subAmount < amount)
+                items = new Item[subAmount];
+            else
+                items = new Item[amount];
+
+            for(int i =0, length = items.Length; i<length; i++)
+            {
+                items[i] = new Item(vecSubscribedItems[i].Value, this);
+            }
+
+            return items;
+        }
 
         /// <summary>
         /// How a query should be ordered.

Facepunch.Steamworks/SteamNative/SteamNative.SteamUGC.cs

@@ -284,9 +284,12 @@ public bool GetQueryUGCStatistic( UGCQueryHandle_t handle /*UGCQueryHandle_t*/,
 		}
 		
 		// uint
-		public uint GetSubscribedItems( PublishedFileId_t* pvecPublishedFileID /*PublishedFileId_t **/, uint cMaxEntries /*uint32*/ )
+		public uint GetSubscribedItems( PublishedFileId_t[] pvecPublishedFileID /*PublishedFileId_t **/, uint cMaxEntries /*uint32*/ )
 		{
-			return platform.ISteamUGC_GetSubscribedItems( (IntPtr) pvecPublishedFileID, cMaxEntries );
+            fixed (PublishedFileId_t* pvecPublishedFileID_ptr = pvecPublishedFileID)
+            {
+                return platform.ISteamUGC_GetSubscribedItems((IntPtr)pvecPublishedFileID_ptr, cMaxEntries);
+            }
 		}
 		
 		// SteamAPICall_t