support for .NET framework 3.5

Still have bugs

Net35/HandyControl_Net35/Shell/Standard/ITaskbarList2.cs

@@ -0,0 +1,17 @@
+namespace Standard
+{
+    using System;
+    using System.Runtime.InteropServices;
+
+    [ComImport, Guid("602D4995-B13A-429b-A66E-1935E44F4317"), InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
+    internal interface ITaskbarList2 : Standard.ITaskbarList
+    {
+        void HrInit();
+        void AddTab(IntPtr hwnd);
+        void DeleteTab(IntPtr hwnd);
+        void ActivateTab(IntPtr hwnd);
+        void SetActiveAlt(IntPtr hwnd);
+        void MarkFullscreenWindow(IntPtr hwnd, [MarshalAs(UnmanagedType.Bool)] bool fFullscreen);
+    }
+}
+