Add custom validate-docx.sh script.

This checks files other than document.xml in a docx container.
Thanks to @edwintorok.

tools/validate-docx.sh

@@ -0,0 +1,21 @@
+#!/bin/sh
+# Modified by edwintorok from https://github.com/devoidfury/docx-validator
+# to look at more files than just document.xml.
+# Further modified by jgm for portability.
+tmpdir=$(mktemp -d)
+errors=0
+for file in "$@"; do
+  echo "*** Checking $file"
+  rm -rf "$tmpdir"
+  unzip -q -o -j "$file" -d "$tmpdir"
+  for i in comments document fontTable footnotes numbering settings styles theme1 webSettings; do
+    xmllint --format "$tmpdir/${i}.xml" > "$tmpdir/${i}-pretty.xml"
+  done
+  XSD="./docx-validator/schemas/microsoft/wml-2010.xsd"
+  for i in "$tmpdir"/*-pretty.xml; do
+    xmllint -noout -nonet \
+      -schema "${XSD}" \
+      "${i}" 2>&1 || errors=$((errors + 1))
+  done
+done
+exit $errors