Add convenience Call ctor for Message

Ooui/EventTarget.cs

@@ -108,12 +108,7 @@ namespace Ooui
 
         protected void SendCall (string methodName, params object[] args)
         {
-            Send (new Message {
+            Send (Message.Call (Id, methodName, args));
-                MessageType = MessageType.Call,
-                TargetId = Id,
-                Key = methodName,
-                Value = args,
-            });
         }
 
         protected void SendSet (string attributeName, object value)

Ooui/Message.cs

@@ -22,6 +22,13 @@ namespace Ooui
         [JsonProperty("v")]
         public object Value = null;
 
+        public static Message Call (string targetId, string method, params object[] args) => new Message {
+            MessageType = MessageType.Call,
+            TargetId = targetId,
+            Key = method,
+            Value = args,
+        };
+
         public static Message Event (string targetId, string eventType) => new Message {
             MessageType = MessageType.Event,
             TargetId = targetId,

Ooui/UI.cs

@@ -353,12 +353,8 @@ namespace Ooui
                     //
                     // Add it to the document body
                     //
-                    await SendMessageAsync (webSocket, new Message {
+                    await SendMessageAsync (webSocket, Message.Call ("document.body", "appendChild", element),
-                        TargetId = "document.body",
+                        element, createdIds, token).ConfigureAwait (false);
-                        MessageType = MessageType.Call,
-                        Key = "appendChild",
-                        Value = new[] { element },
-                    }, element, createdIds, token).ConfigureAwait (false);
 
                     //
                     // Listen for events