Add compile options to turn off features

Ooui/Element.cs

@@ -232,6 +232,8 @@ namespace Ooui
 
         protected virtual bool HtmlNeedsFullEndElement => false;
 
+#if !NO_XML
+
         public override void WriteOuterHtml (System.Xml.XmlWriter w)
         {
             w.WriteStartElement (TagName);
@@ -262,5 +264,7 @@ namespace Ooui
                 c.WriteOuterHtml (w);
             }
         }
+
+#endif
     }
 }

Ooui/Node.cs

@@ -188,6 +188,8 @@ namespace Ooui
             return false;
         }
 
+#if !NO_XML
+
         public virtual string OuterHtml {
             get {
                 using (var stream = new System.IO.MemoryStream ()) {
@@ -206,6 +208,8 @@ namespace Ooui
         }
 
         public abstract void WriteOuterHtml (System.Xml.XmlWriter w);
+
+#endif
     }
 
     class ReadOnlyList<T> : IReadOnlyList<T>

Ooui/TextArea.cs

@@ -55,9 +55,13 @@ namespace Ooui
             return base.TriggerEventFromMessage (message);
         }
 
+#if !NO_XML
+
         public override void WriteInnerHtml (System.Xml.XmlWriter w)
         {
             w.WriteString (val ?? "");
         }
+
+#endif
     }
 }

Ooui/TextNode.cs

@@ -21,9 +21,13 @@ namespace Ooui
             Text = text;
         }
 
+#if !NO_XML
+
         public override void WriteOuterHtml (System.Xml.XmlWriter w)
         {
             w.WriteString (text);
         }
+
+#endif
     }
 }