support for .NET framework 3.5

Still have bugs

Net35/HandyControlDemo_Net35/UserControl/Controls/CoverFlowDemoCtl.xaml

@@ -0,0 +1,7 @@
+<UserControl x:Class="HandyControlDemo.UserControl.CoverFlowDemoCtl"
+             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:controls="clr-namespace:HandyControl.Controls;assembly=HandyControl"
+             Background="{DynamicResource RegionBrush}">
+    <controls:CoverFlow x:Name="CoverFlowMain" Margin="32" Width="500" Height="300"/>
+</UserControl>