Convert docdock theme from submodule to native files and fix Hugo compatibility

themes/docdock/layouts/shortcodes/relref.html

@@ -0,0 +1,14 @@
+{{- if in (.Get 0) "/_index.md" -}}
+	{{- $paths := (split (.Get 0) "_index.md") -}}
+	{{- $pagepath := index $paths 0 -}}
+	{{- $anchor := index $paths 1 -}}
+	{{- with .Site.GetPage "section" (trim $pagepath "/") -}}
+		{{- ( printf "%s%s" $pagepath $anchor ) | relLangURL -}}
+	{{- end -}}
+{{- else -}}
+	{{- with .Site.GetPage "section" (.Get 0) }}
+		{{- .RelPermalink -}}
+	{{- else -}}
+		{{- .Get 0 | relref .Page -}}
+	{{- end -}}
+{{- end -}}