support for .NET framework 3.5

Still have bugs

Net35/HandyControl_Net35/Shell/Standard/HIGHCONTRAST.cs

@@ -0,0 +1,14 @@
+namespace Standard
+{
+    using System;
+    using System.Runtime.InteropServices;
+
+    [StructLayout(LayoutKind.Sequential)]
+    internal struct HIGHCONTRAST
+    {
+        public int cbSize;
+        public Standard.HCF dwFlags;
+        public IntPtr lpszDefaultScheme;
+    }
+}
+