add Screenshot

src/Shared/HandyControl_Shared/Controls/Screenshot/Screenshot.cs

@@ -0,0 +1,16 @@
+using System;
+using System.Windows.Media;
+
+namespace HandyControl.Controls
+{
+    public class Screenshot
+    {
+        public event EventHandler Snapped;
+
+        public ImageSource Source { get; set; }
+
+        public void Start() => new ScreenshotWindow(this).Show();
+
+        internal void OnSnapped() => Snapped?.Invoke(this, EventArgs.Empty);
+    }
+}