Fix RetreiveState, add VoidStatement

Return value from RetrieveState() did not include the fetched document.
Added VoidStatement() method.

Author: cawerkenthin

TinCan/RemoteLRS.cs

@@ -524,6 +524,23 @@ public StatementsResultLRSResponse MoreStatements(StatementsResult result)
 
             return r;
         }
+        
+        public StatementLRSResponse VoidStatement(Guid id, Agent agent)
+        {
+            var voidStatement = new Statement
+            {
+                actor = agent,
+                verb = new Verb
+                {
+                    id = new Uri("http://adlnet.gov/expapi/verbs/voided"),
+                    display = new LanguageMap()
+                },
+                target = new StatementRef { id = id }
+            };
+            voidStatement.verb.display.Add("en-US", "voided");
+
+            return SaveStatement(voidStatement);
+        }
 
         // TODO: since param
         public ProfileKeysLRSResponse RetrieveStateIds(Activity activity, Agent agent, Nullable<Guid> registration = null)
@@ -567,6 +584,7 @@ public StateLRSResponse RetrieveState(String id, Activity activity, Agent agent,
                 return r;
             }
             r.success = true;
+            r.content = state;
 
             return r;
         }