add Loading doc

src/Shared/HandyControl_Shared/Controls/Input/DateTimePicker.cs

@@ -74,7 +74,7 @@ namespace HandyControl.Controls
         {
             EventManager.RegisterClassHandler(typeof(DateTimePicker), GotFocusEvent, new RoutedEventHandler(OnGotFocus));
             KeyboardNavigation.TabNavigationProperty.OverrideMetadata(typeof(DateTimePicker), new FrameworkPropertyMetadata(KeyboardNavigationMode.Once));
-            KeyboardNavigation.IsTabStopProperty.OverrideMetadata(typeof(DateTimePicker), new FrameworkPropertyMetadata(false));
+            KeyboardNavigation.IsTabStopProperty.OverrideMetadata(typeof(DateTimePicker), new FrameworkPropertyMetadata(ValueBoxes.FalseBox));
         }
 
         public DateTimePicker()

src/Shared/HandyControl_Shared/Controls/Input/TimePicker.cs

@@ -72,7 +72,7 @@ namespace HandyControl.Controls
         {
             EventManager.RegisterClassHandler(typeof(TimePicker), GotFocusEvent, new RoutedEventHandler(OnGotFocus));
             KeyboardNavigation.TabNavigationProperty.OverrideMetadata(typeof(TimePicker), new FrameworkPropertyMetadata(KeyboardNavigationMode.Once));
-            KeyboardNavigation.IsTabStopProperty.OverrideMetadata(typeof(TimePicker), new FrameworkPropertyMetadata(false));
+            KeyboardNavigation.IsTabStopProperty.OverrideMetadata(typeof(TimePicker), new FrameworkPropertyMetadata(ValueBoxes.FalseBox));
         }
 
         public TimePicker()

src/Shared/HandyControl_Shared/Controls/Loading/LoadingCircle.cs

@@ -23,7 +23,7 @@ namespace HandyControl.Controls
 
         public static readonly DependencyProperty NeedHiddenProperty = DependencyProperty.Register(
             "NeedHidden", typeof(bool), typeof(LoadingCircle),
-            new FrameworkPropertyMetadata(true, FrameworkPropertyMetadataOptions.AffectsRender));
+            new FrameworkPropertyMetadata(ValueBoxes.TrueBox, FrameworkPropertyMetadataOptions.AffectsRender));
 
         public bool NeedHidden
         {

src/Shared/HandyControl_Shared/Controls/Other/AnimationPath.cs

@@ -80,7 +80,7 @@ namespace HandyControl.Controls
         }
 
         public static readonly DependencyProperty IsPlayingProperty = DependencyProperty.Register(
-            "IsPlaying", typeof(bool), typeof(AnimationPath), new FrameworkPropertyMetadata(true, (o, args) =>
+            "IsPlaying", typeof(bool), typeof(AnimationPath), new FrameworkPropertyMetadata(ValueBoxes.TrueBox, (o, args) =>
             {
                 var ctl = (AnimationPath)o;
                 var v = (bool)args.NewValue;