Add support for Export Snippets and Export Blocks

Now these work:

* Export Snippets

  @@hugo:foo@@

* Export Blocks

  #+BEGIN_EXPORT hugo
  foo
  #+END_EXPORT

ox-hugo.el

@@ -606,6 +606,8 @@ newer."
               (org-hugo-export-as-md a s v)))))
   :translate-alist '((code . org-hugo-kbd-tags-maybe)
                      (example-block . org-hugo-example-block)
+                     (export-block . org-hugo-export-block)
+                     (export-snippet . org-hugo-export-snippet)
                      (headline . org-hugo-headline)
                      (inner-template . org-hugo-inner-template)
                      (keyword . org-hugo-keyword)
@@ -988,6 +990,36 @@ information."
           (format "{{< highlight text %s>}}\n%s{{< /highlight >}}\n" linenos-str text))
       (org-blackfriday-example-block example-block nil info))))
 
+;;;; Export Snippet
+(defun org-hugo-export-snippet (export-snippet _contents _info)
+  "Transcode a EXPORT-SNIPPET object from Org to Hugo-compatible Markdown.
+CONTENTS is nil.  INFO is a plist holding contextual information.
+
+Example:
+
+  \"@@hugo:foo@@\"
+
+exports verbatim to \"foo\" only when exported using `hugo'
+backend."
+  (when (eq (org-export-snippet-backend export-snippet) 'hugo)
+    (org-element-property :value export-snippet)))
+
+;;;; Export Block
+(defun org-hugo-export-block (export-block _contents info)
+  "Transcode a EXPORT-BLOCK element from Org to Hugo-compatible Markdown.
+CONTENTS is nil.  INFO is a plist holding contextual information.
+
+Example:
+
+  #+BEGIN_EXPORT hugo
+  foo
+  #+END_EXPORT
+
+exports verbatim to \"foo\" only when exported using `hugo'
+backend."
+  (when (string= (org-element-property :type export-block) "HUGO")
+    (org-element-property :value export-block)))
+
 ;;;; Headline
 (defun org-hugo-headline (headline contents info)
   "Transcode HEADLINE element into Markdown format.

test/site/content-org/all-posts.org

@@ -2638,6 +2638,16 @@ The front-matter for this post contains the default Creator string.
 :EXPORT_FILE_NAME: custom-creator
 :END:
 The front-matter for this post contains a custom Creator string.
+* Export snippets and blocks                    :export_snippet:export_block:
+:PROPERTIES:
+:EXPORT_FILE_NAME: export_snippets_and_blocks
+:END:
+** Export snippet
+@@hugo:This will get exported only for Hugo exports, `verbatim`.@@
+** Export block
+#+BEGIN_EXPORT hugo
+and **this too**.. `verbatim`.
+#+END_EXPORT
 * Miscellaneous Front Matter                                   :front_matter:
 ** Hugo Aliases                                                     :aliases:
 *** Alias without section portion 1

test/site/content/posts/export_snippets_and_blocks.md

@@ -0,0 +1,14 @@
++++
+title = "Export snippets and blocks"
+tags = ["export-snippet", "export-block"]
+draft = false
++++
+
+## Export snippet {#export-snippet}
+
+This will get exported only for Hugo exports, `verbatim`.
+
+
+## Export block {#export-block}
+
+and **this too**.. `verbatim`.