support for .NET framework 3.5

Still have bugs

Net35/HandyControlDemo_Net35/UserControl/Controls/TextBoxDemoCtl.xaml.cs

@@ -0,0 +1,10 @@
+namespace HandyControlDemo.UserControl
+{
+    public partial class TextBoxDemoCtl
+    {
+        public TextBoxDemoCtl()
+        {
+            InitializeComponent();
+        }
+    }
+}