feat: add mermaid code fences usage

assets/js/clipboard.js

@@ -5,7 +5,11 @@ var pre = document.getElementsByTagName('pre');
 for (var i = 0; i < pre.length; ++ i)
 {
   var element = pre[i];
-  element.insertAdjacentHTML('afterbegin', '<button class="btn btn-copy"></button>');
+  var mermaid = element.getElementsByClassName('language-mermaid')[0];
+
+  if (mermaid == null) {
+    element.insertAdjacentHTML('afterbegin', '<button class="btn btn-copy"></button>');
+  }
 }
 
 var clipboard = new Clipboard('.btn-copy', {

assets/js/mermaid.js

@@ -7,4 +7,5 @@ var config = {
 
 document.addEventListener('DOMContentLoaded', () => {
   mermaid.initialize(config);
+  mermaid.init(undefined, '.language-mermaid');
 });