add support for Mermaid diagrams

layouts/_default/_markup/render-codeblock-mermaid.html

@@ -0,0 +1,4 @@
+<pre class="mermaid">
+  {{- .Inner | safeHTML }}
+</pre>
+{{ .Page.Store.Set "hasMermaid" true }}

layouts/_default/single.html

@@ -70,6 +70,14 @@
     {{ end }}
   </div>
 
+  {{ if .Store.Get "hasMermaid" }}
+  <script type="module">
+    import mermaid from 'https://cdn.jsdelivr.net/npm/mermaid/dist/mermaid.esm.min.mjs';
+    mermaid.initialize({ startOnLoad: true });
+  </script>
+  {{ end }}
+
+
   {{/* Next prev controls */}}
 
   {{ if not (.Param "hidePagination") }}
@@ -88,4 +96,4 @@
 
 </div>
 
-{{ end }}
+{{ end }}