Implementing the rest of the Notifications API

Octokit/Models/Request/MarkAsReadRequest.cs

@@ -0,0 +1,20 @@
+using System;
+using System.Diagnostics;
+using Octokit.Internal;
+
+namespace Octokit
+{
+    [DebuggerDisplay("{DebuggerDisplay,nq}")]
+    public class MarkAsReadRequest : RequestParameters
+    {
+        public MarkAsReadRequest()
+        {
+            LastReadAt = null;
+        }
+
+        /// <summary>
+        /// Describes the last point that notifications were checked. Anything updated since this time will not be updated.
+        /// </summary>
+        public DateTimeOffset? LastReadAt { get; set; }
+    }
+}