First letterSpacing implementation attempt

lib/attributes.js

@@ -23,7 +23,9 @@ function fontDiffer(a, b) {
     return a.fontSize !== b.fontSize ||
         a.fontFamily !== b.fontFamily ||
         a.fontStyle !== b.fontStyle ||
-        a.fontWeight !== b.fontWeight;
+        a.fontWeight !== b.fontWeight ||
+        a.kerning !== b.kerning ||
+        a.letterSpacing !== b.letterSpacing;
 }
 
 const ViewBoxAttributes = {

lib/extract/extractText.js

@@ -55,7 +55,9 @@ export function extractFont(props) {
         fontFamily: extractSingleFontFamily(props.fontFamily),
         fontSize: isNaN(fontSize) ? null : fontSize,
         fontWeight: props.fontWeight,
-        fontStyle: props.fontStyle
+        fontStyle: props.fontStyle,
+        kerning: props.kerning,
+        letterSpacing: props.letterSpacing,
     };
 
     if (typeof props.font === 'string') {

lib/props.js

@@ -53,6 +53,8 @@ const fontProps = {
     fontSize: numberProp,
     fontWeight: numberProp,
     fontStyle: PropTypes.string,
+    letterSpacing: PropTypes.string,
+    kerning: PropTypes.string,
     font: PropTypes.object
 };