Added X-WNS-PRIORITY header for WNS notifications

PushSharp.Windows/WnsConnection.cs

@@ -64,7 +64,10 @@ public async Task Send (WnsNotification notification)
 
             http.DefaultRequestHeaders.TryAddWithoutValidation ("X-WNS-Type", string.Format ("wns/{0}", notification.Type.ToString().ToLower ()));
 
-            if(!http.DefaultRequestHeaders.Contains("Authorization")) //prevent double values
+            if (notification.Priority != WnsPriority.Unspecified)
+                http.DefaultRequestHeaders.TryAddWithoutValidation("X-WNS-PRIORITY", ((int)notification.Priority).ToString());
+
+            if (!http.DefaultRequestHeaders.Contains("Authorization")) //prevent double values
                 http.DefaultRequestHeaders.TryAddWithoutValidation("Authorization", "Bearer " + accessToken);
 
             if (notification.RequestForStatus.HasValue)

PushSharp.Windows/WnsNotification.cs

@@ -14,6 +14,8 @@ public abstract class WnsNotification : INotification
 
         public abstract WnsNotificationType Type { get; }
 
+        public WnsPriority Priority { get; set; }
+
         public bool IsDeviceRegistrationIdValid ()
         {
             return true;

PushSharp.Windows/WnsNotificationStatus.cs

@@ -43,5 +43,14 @@ public enum WnsNotificationType
         Toast,
         Raw
     }
+
+    public enum WnsPriority
+    {
+        Unspecified = 0,
+        High = 1,
+        Meduim = 2,
+        Low = 3,
+        VeryLow = 4
+    }
 }