Implement correct path measurement, matrix calculation, getTextAnchorShift, startOffset.

Add method and spacing attributes to textPath.
Correct startOffset calculation.
Implement method="stretch".

lib/attributes.js

@@ -114,6 +114,8 @@ const TextAttributes = {
 
 const TextPathAttributes = {
     href: true,
+    method: true,
+    spacing: true,
     startOffset: true,
     ...RenderableAttributes
 };

lib/extract/extractText.js

@@ -91,6 +91,8 @@ export default function(props, container) {
         y,
         dx,
         dy,
+        method,
+        spacing,
         textAnchor,
         startOffset
     } = props;
@@ -127,6 +129,8 @@ export default function(props, container) {
         content,
         deltaX,
         deltaY,
+        method,
+        spacing,
         startOffset: (startOffset || 0).toString(),
         positionX: _.isNil(x) ? null : x.toString(),
         positionY: _.isNil(y) ? null : y.toString()