support for .NET framework 3.5

Still have bugs

Net35/HandyControl_Net35/Shell/Standard/ITaskbarList.cs

@@ -0,0 +1,16 @@
+namespace Standard
+{
+    using System;
+    using System.Runtime.InteropServices;
+
+    [ComImport, Guid("56FDF342-FD6D-11d0-958A-006097C9A090"), InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
+    internal interface ITaskbarList
+    {
+        void HrInit();
+        void AddTab(IntPtr hwnd);
+        void DeleteTab(IntPtr hwnd);
+        void ActivateTab(IntPtr hwnd);
+        void SetActiveAlt(IntPtr hwnd);
+    }
+}
+