Fixing Build Errors

Source/DataTypes/SvgAspectRatioConverter.cs

@@ -4,7 +4,6 @@ using System.ComponentModel;
 using System.Globalization;
 using System.Linq;
 using System.Text;
-using System.Threading.Tasks;
 
 namespace Svg.DataTypes
 {
@@ -38,8 +37,13 @@ namespace Svg.DataTypes
                     throw new ArgumentOutOfRangeException("value is not a member of SvgPreserveAspectRatio");
             }
 
+#if Net4
             if (!Enum.TryParse<SvgPreserveAspectRatio>(sParts[nAlignIndex], out eAlign))
                 throw new ArgumentOutOfRangeException("value is not a member of SvgPreserveAspectRatio");
+#else
+            eAlign = (SvgPreserveAspectRatio)Enum.Parse(typeof(SvgPreserveAspectRatio), sParts[nAlignIndex]);
+#endif
+
             nAlignIndex++;
 
             if (sParts.Length > nAlignIndex)

Source/DataTypes/SvgOrient.cs

 using Svg.DataTypes;
 using System.ComponentModel;
+using System;
 
 namespace Svg
 {

Source/Painting/SvgMarker.cs

@@ -85,13 +85,6 @@ namespace Svg
 			set { this.Attributes["markerHeight"] = value; }
 		}
 
-		[SvgAttribute("markerUnits")]
-		public virtual SvgMarkerUnits MarkerUnits
-		{
-			get { return this.Attributes.GetAttribute<SvgMarkerUnits>("markerUnits"); }
-			set { this.Attributes["markerUnits"] = value; }
-		}
-
 		public SvgMarker()
 		{
 			MarkerUnits = SvgMarkerUnits.strokeWidth;