Returned ReadOnlyTopicCollection

Previously returned the generic interface. Since we know the results will be of type `Topic` (or descendants), it is simpler to return simply `ReadOnlyTopicCollection`. This is also more consistent with .NET Framework Design Guidelines.

Author: JeremyCaney

Ignia.Topics/Collections/RelatedTopicCollection.cs

@@ -71,8 +71,8 @@ public ReadOnlyCollection<string> Keys {
     /// <returns>
     ///   Returns an enumerable list of <see cref="Topic"/> objects.
     /// </returns>
-    public ReadOnlyTopicCollection<Topic> GetAllTopics() {
-      Contract.Ensures(Contract.Result<ReadOnlyTopicCollection<Topic>>() != null);
+    public ReadOnlyTopicCollection GetAllTopics() {
+      Contract.Ensures(Contract.Result<ReadOnlyTopicCollection>() != null);
       var topics = new TopicCollection();
       foreach (var topicCollection in this) {
         foreach (var topic in topicCollection) {
@@ -81,7 +81,7 @@ public ReadOnlyTopicCollection<Topic> GetAllTopics() {
           }
         }
       }
-      return new ReadOnlyTopicCollection<Topic>(topics);
+      return new ReadOnlyTopicCollection(topics);
     }
 
     /// <summary>
@@ -90,10 +90,10 @@ public ReadOnlyTopicCollection<Topic> GetAllTopics() {
     /// <returns>
     ///   Returns an enumerable list of <see cref="Topic"/> objects.
     /// </returns>
-    public ReadOnlyTopicCollection<Topic> GetAllTopics(string contentType) {
-      Contract.Ensures(Contract.Result<ReadOnlyTopicCollection<Topic>>() != null);
+    public ReadOnlyTopicCollection GetAllTopics(string contentType) {
+      Contract.Ensures(Contract.Result<ReadOnlyTopicCollection>() != null);
       var topics = GetAllTopics().Where(t => t.ContentType == contentType);
-      return ReadOnlyTopicCollection<Topic>.FromList(topics.ToList());
+      return ReadOnlyTopicCollection.FromList(topics.ToList());
     }
 
     /*==========================================================================================================================