Fix #undefined named anchors for question permalinks. Resolve #304

Also removed comment from the default config which made it invalid JSON.
(The same explanation is already included in README)

config/default.json

@@ -1,14 +1,4 @@
 {
 	"indexConfig": {
-		// this config is used during the build to configure Zotero Bib
-		// component both during development and in production. Values
-		// listed below can be overriden in local.json and/or using
-		// env variables. See https://www.npmjs.com/package/config
-		// 
-		// "apiAuthorityPart": undefined,
-		// "storeURL": undefined,
-		// "stylesURL": undefined,
-		// "translatePrefix": "",
-		// "translateURL": undefined
 	}
 }

scripts/build-html.cjs

@@ -13,7 +13,9 @@ const addAnchors = html => {
 	const $ = cheerio.load(html);
 	const headers = $('h2, h3');
 	headers.map((_, element) => {
-		const id = element.attribs.id;
+		const id = element.attribs.id ?? $(element).text().replace(/[^\w\s]/g, '').trim().replace(/\s/g, '_').toLocaleLowerCase();
+		element.attribs.id = id;
+
 		$('<a>')
 			.attr('href', '#' + id)
 			.addClass('anchor-link')