New: (RuTracker) Search by Categories

src/NzbDrone.Core/Indexers/Definitions/RuTracker.cs

@@ -1443,6 +1443,11 @@ namespace NzbDrone.Core.Indexers.Definitions
                 queryCollection.Add("nm", searchString);
             }
 
+            if (categories.Length > 0)
+            {
+                queryCollection.Add("f", string.Join(",", Capabilities.Categories.MapTorznabCapsToTrackers(categories)));
+            }
+
             searchUrl = searchUrl + "?" + queryCollection.GetQueryString();
 
             var request = new IndexerRequest(searchUrl, HttpAccept.Html);