Heading render hook: support all attributes (#2206)

Author: chalin

layouts/_default/_markup/td-render-heading.html

@@ -1,5 +1,7 @@
-<h{{ .Level }} id="{{ .Anchor | safeURL }}"
-  {{- with .Attributes.class }} class="{{ . }}" {{- end -}}
+<h{{ .Level }}
+  {{- range $key, $value := .Attributes -}}
+    {{ printf " %s=%q" $key (string $value) | safeHTMLAttr -}}
+  {{ end -}}
 >
   {{- .Text | safeHTML -}}
   {{ template "_default/_markup/_td-heading-self-link.html" . -}}

userguide/content/en/docs/adding-content/navigation.md

@@ -341,7 +341,6 @@ cascade:
 ```
 
 ## Heading self links
-{.test-class}
 
 Docsy supports build-time generation of heading self links using Hugo's
 `render-heading.html` [hook].