Record the WOFF 2.0 compression improvement (%) in the CSV file

src/com/google/typography/font/compression/CompressionStats.java

@@ -72,6 +72,12 @@ public class CompressionStats {
       return sizes.get(size);
     }
 
+    public double getPercent(Size s1, Size s2) {
+      long v1 = sizes.get(s1);
+      long v2 = sizes.get(s2);
+      return 100.0 * (v1 - v2) / v1;
+    }
+
     public static Builder builder() {
       return new Builder();
     }

src/com/google/typography/font/compression/CsvReport.java

@@ -17,13 +17,14 @@ public class CsvReport {
   public static void create(CompressionStats stats, String filename) throws IOException {
     PrintWriter writer = new PrintWriter(new BufferedWriter(new FileWriter(filename)));
     try {
-      writer.printf("Font, Original, GZIP, WOFF 2.0\n");
+      writer.printf("'Font', 'Original (bytes)', 'GZIP (bytes)', 'WOFF 2.0 (bytes)', '%% Improvement'\n");
       for (CompressionStats.Stats stat : stats.values()) {
-        writer.printf("%s, %d, %d, %d\n",
+        writer.printf("%s, %d, %d, %d, %.2f%%\n",
             stat.getFilename(),
             stat.getSize(CompressionStats.Size.ORIGINAL),
             stat.getSize(CompressionStats.Size.GZIP),
-            stat.getSize(CompressionStats.Size.WOFF2));
+            stat.getSize(CompressionStats.Size.WOFF2),
+            stat.getPercent(CompressionStats.Size.GZIP, CompressionStats.Size.WOFF2));
       }
     } finally {
       Closeables.closeQuietly(writer);