Enable highlighting of code blocks using highlight.js

Makefile

@@ -7,6 +7,7 @@ install: .allow-install
 js: js/package-lock.json
 	( cd js && node_modules/.bin/browserify -o ../static/bundle.js owl.js --standalone owl --plugin tinyify )
 	cp js/node_modules/katex/dist/katex.min.css static/
+	cp js/node_modules/highlight.js/styles/github.css static/
 	rm -rf static/fonts && cp -a js/node_modules/katex-fonts/fonts static/
 
 js/package-lock.json: js/package.json

js/owl.js

-var md = require('markdown-it')()
-var mk = require('markdown-it-katexx')
-
+const md = require('markdown-it')()
 md.set({
 	html: false,
 	typographer: true,
-});
+})
+
+const mk = require('markdown-it-katexx')
+md.use(mk);
 
-md.use(mk)
+const hljs = require('highlight.js/lib/core')
+hljs.registerLanguage('plaintext', require('highlight.js/lib/languages/plaintext'))
+hljs.registerLanguage('c', require('highlight.js/lib/languages/c'))
+hljs.registerLanguage('cpp', require('highlight.js/lib/languages/cpp'))
+hljs.registerLanguage('python', require('highlight.js/lib/languages/python'))
+hljs.registerLanguage('haskell', require('highlight.js/lib/languages/haskell'))
+hljs.registerLanguage('prolog', require('highlight.js/lib/languages/prolog'))
+
+const mhl = require('markdown-it-highlightjs/core')
+md.use(mhl, {
+	auto: false,
+	code: true,
+	inline: false,
+	hljs: hljs,
+});
 
 exports.render_md = function () {
 	console.log('Owl: Rendering Markdown');

js/package.json

@@ -9,6 +9,7 @@
     "katex": "^0.12.0",
     "katex-fonts": "katex/katex-fonts",
     "markdown-it": ">=11.0",
+    "markdown-it-highlightjs": ">=3.4.0",
     "markdown-it-katexx": ">=3.2.0",
     "browserify": ">=16.5",
     "tinyify": "browserify/tinyify"