Move default highlight.js highlighting into a web worker

Author: Steve Day

public/js/highlight.js

@@ -0,0 +1,7 @@
+// A very simple web worker for highlight.js
+// See: https://highlightjs.org/usage/
+onmessage = function(event) {
+    importScripts('/vendor/plugins/highlight/highlight.pack.js');
+    var result = self.hljs.highlightAuto(event.data);
+    postMessage(result.value);
+}

public/js/index.js

@@ -1430,7 +1430,13 @@ $(document).ready(function () {
 
     // Highlight JS
     if (typeof hljs != 'undefined') {
-        hljs.initHighlightingOnLoad();
+        $('pre code').each(function (index, element) {
+            var worker = new Worker('/js/highlight-worker.js');
+            worker.onmessage = function(event) {
+                $(element).html(event.data);
+            }
+            worker.postMessage($(element).text());
+        });
     }
 
     // Dropzone