Add TextPath element

lib/attributes.js

@@ -98,6 +98,10 @@ const TextAttributes = merge({
     positionY: true
 }, RenderableAttributes);
 
+const TextPathAttributes = {
+    href: true
+};
+
 const TSpanAttibutes = merge({
     content: true
 }, TextAttributes);
@@ -173,6 +177,7 @@ export {
     PathAttributes,
     TextAttributes,
     TSpanAttibutes,
+    TextPathAttributes,
     GroupAttributes,
     ClipPathAttributes,
     CircleAttributes,