Help with proper toc labeling (#86)

Particularly to fix casing if somebody does "Table of Contents"

src/scripts/pre-commit-toc.js

@@ -17,12 +17,41 @@ from https://github.com/jonschlinkert/markdown-toc.
 const mdtoc = require('markdown-toc');
 const fs = require('fs');
 
+var error = 0;
 const files = process.argv.slice(2);
 for (var i = 0; i < files.length; ++i) {
-  const oldContent = fs.readFileSync(files[i]).toString();
-  const newContent = mdtoc.insert(oldContent, { bullets: '-' });
+  const file = files[i];
+  const oldContent = fs.readFileSync(file).toString();
+  var newContent = oldContent;
+
+  // Only process files with the toc indicator.
+  if (!oldContent.match(/<!-- toc -->/m)) continue;
+
+  // If there's a case-incorrect toc section, fix casing.
+  newContent = newContent.replace(
+    /\n## Table of contents\n\n<!-- toc -->\n/im,
+    '\n## Table of contents\n\n<!-- toc -->\n'
+  );
   if (oldContent != newContent) {
-    console.log(`Updating ${files[i]}`);
-    fs.writeFileSync(files[i], newContent);
+    console.log(`Fixed "Table of contents" header in ${file}`);
+  }
+
+  // Ensure the file properly labels the toc.
+  if (!newContent.match(/\n## Table of contents\n\n<!-- toc -->\n/m)) {
+    error = 1;
+    console.log(
+      `${file} has a toc without a "Table of contents" header. Use:\n` +
+        '  ## Table of contents\n\n  <!-- toc -->\n'
+    );
+    continue;
+  }
+
+  // Do the toc substitution.
+  newContent = mdtoc.insert(newContent, { bullets: '-' });
+
+  if (oldContent != newContent) {
+    console.log(`Updating ${file}`);
+    fs.writeFileSync(file, newContent);
   }
 }
+process.exit(error);