Add a script to help diff rendered books

tools/megadiff.sh

@@ -0,0 +1,22 @@
+#!/bin/bash
+
+set -eu
+
+# Remove files that are never affected by rustfmt or are otherwise uninteresting
+rm -rf tmp/book-before/css/ tmp/book-before/theme/ tmp/book-before/img/ tmp/book-before/*.js \
+       tmp/book-before/FontAwesome tmp/book-before/*.css tmp/book-before/*.png \
+       tmp/book-before/*.json tmp/book-before/print.html
+
+rm -rf tmp/book-after/css/ tmp/book-after/theme/ tmp/book-after/img/ tmp/book-after/*.js \
+      tmp/book-after/FontAwesome tmp/book-after/*.css tmp/book-after/*.png \
+      tmp/book-after/*.json tmp/book-after/print.html
+
+# Get all the html files before
+ls tmp/book-before/*.html | \
+# Extract just the filename so we can reuse it easily.
+xargs -n 1 basename | \
+while IFS= read -r filename; do
+    # Remove any files that are the same before and after
+    diff "tmp/book-before/$filename" "tmp/book-after/$filename" > /dev/null \
+      && rm "tmp/book-before/$filename" "tmp/book-after/$filename"
+done