Fixed some typos in comments and done some minor cleanup.

Author: otuncelli

SvgFileType/LayersMode.cs

@@ -1,10 +1,4 @@
-using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Text;
-using System.Threading.Tasks;
-
-namespace SvgFileTypePlugin
+namespace SvgFileTypePlugin
 {
     public enum LayersMode
     {

SvgFileType/PaintGroupBoundaries.cs

@@ -0,0 +1,25 @@
+using Svg;
+using System;
+using System.Drawing;
+using System.Drawing.Drawing2D;
+
+namespace SvgFileTypePlugin
+{
+    // Used to determine boundaries of a group.
+    public class PaintGroupBoundaries : SvgVisualElement
+    {
+        public SvgGroup RelatedGroup { get; set; }
+        public bool IsStart { get; set; }
+        public override RectangleF Bounds => throw new NotImplementedException();
+
+        public override SvgElement DeepCopy()
+        {
+            throw new NotImplementedException();
+        }
+
+        public override GraphicsPath Path(ISvgRenderer renderer)
+        {
+            throw new NotImplementedException();
+        }
+    }
+}