Add method to get the sent messages

Author: Suiram1701

API.Test/MessagesTests.cs

@@ -49,6 +49,19 @@ public void GetMessageInbox()
             Assert.Fail();
     }
 
+    [Test]
+    public void GetSentMessages()
+    {
+        Client.LoginAsync(s_Server, s_LoginName, s_UserName, s_Password).Wait();
+
+        Task<MessagePreview[]> messages = Client.GetSentMessagesAsync();
+        messages.Wait();
+        if (messages.Result != null)
+            Assert.Pass();
+        else
+            Assert.Fail();
+    }
+
     [Test]
     public void GetFullMessage()
     {

WebUntisAPI.Client/WebUntisClient.Messages.cs

@@ -80,6 +80,22 @@ public async Task<MessagePreview[]> GetMessageInboxAsync(CancellationToken ct =
             return new JsonSerializer().Deserialize<List<MessagePreview>>(jsonMsg.CreateReader()).ToArray();
         }
 
+        /// <summary>
+        /// Get the sent messages
+        /// </summary>
+        /// <param name="ct">Cancellation token</param>
+        /// <returns>The sent messages</returns>
+        /// <exception cref="ObjectDisposedException">Thrown when the instance was disposed</exception>
+        /// <exception cref="UnauthorizedAccessException">Thrown when you're logged in</exception>
+        /// <exception cref="HttpRequestException">Thrown when an error happened while the http request</exception>
+        public async Task<MessagePreview[]> GetSentMessagesAsync(CancellationToken ct = default)
+        {
+            string responseString = await MakeAPIGetRequestAsync("/WebUntis/api/rest/view/v1/messages/sent", ct);
+
+            JArray jsonMsg = JObject.Parse(responseString).Value<JArray>("sentMessages");
+            return new JsonSerializer().Deserialize<List<MessagePreview>>(jsonMsg.CreateReader()).ToArray();
+        }
+
         /// <summary>
         /// Send a draft
         /// </summary>