graphviz: allow overriding the engine

This can be done like so:

  {{< graphviz engine="neato" >}}

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

layouts/_default/baseof.html

@@ -202,6 +202,7 @@ <h1 data-pagefind-meta="title">About{{ if (isset .Params "subtitle") }} - {{ .Pa
         graphAttributes: {
           bgcolor: "transparent",
         },
+        engine: x.getAttribute("engine") || "dot",
       }
       const svg = vizInstance.renderSVGElement(x.innerText, options)
       svg.classList.add("graphviz")

layouts/shortcodes/graphviz.html

@@ -1,4 +1,4 @@
-<pre class="graphviz">
+<pre class="graphviz"{{ if (ne "" (.Get "engine")) }} engine="{{(.Get "engine")}}"{{ end }}>
   {{ .Inner | htmlEscape | safeHTML }}
 </pre>
 {{ .Page.Store.Set "hasGraphviz" true }}