Generate source offset in HTML

Signed-off-by: Danila Fedorin <danila.fedorin@gmail.com>

layouts/partials/highlightgroup.html

@@ -6,4 +6,7 @@
 {{- if eq (lower .language) "agda" -}}
 {{- $scratch.Add "highlightGroupAttrs" " data-agda-block" -}}
 {{- end -}}
+{{- with .offset -}}
+{{- $scratch.Add "highlightGroupAttrs" (printf " data-source-offset=\"%v\"" .) -}}
+{{- end -}}
 {{ partial "group.html" (dict "url" .url "path" .path "comment" .comment "content" (highlight .code .language .opts) "attrs" ($scratch.Get "highlightGroupAttrs")) }}

layouts/shortcodes/codelines.html

@@ -51,6 +51,7 @@
        "firstLine" (int (.Get 2))
        "lastLine" (int (.Get 3))
        "language" (.Get 0)
+       "offset" ($scratch.Get "prefixLength")
        "opts" (printf "linenos=table,linenostart=%d%s" (.Get 2) ($scratch.Get "opts"))
 -}}
 {{- partial "highlightgroup.html" $groupconfig -}}