Support html and md backend tagged export snippets and export blocks

Now export snippets and export blocks tagged with "md", "markdown" or
"html" get exported by ox-hugo as well.

Fixes https://github.com/kaushalmodi/ox-hugo/issues/107

ox-hugo.el

@@ -1000,12 +1000,22 @@ 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)))
+backend.
+
+Export snippets with backend tags \"markdown:\" and \"md:\" are
+also handled.  Exporting of export snippets with backend tag
+\"html:\" uses the HTML exporter."
+  (cond
+   ((member (org-export-snippet-backend export-snippet) '(hugo markdown md))
+    ;; ox-md.el does not support export snippets, so let's handle
+    ;; Markdown export snippets here as well.
+    (org-element-property :value export-snippet))
+   ;; Also include HTML export snippets.
+   (t
+    (org-export-with-backend 'html export-snippet nil nil))))
 
 ;;;; Export Block
-(defun org-hugo-export-block (export-block _contents info)
+(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.
 
@@ -1016,9 +1026,17 @@ Example:
   #+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)))
+backend.
+
+If the backend tag is \"markdown\"/\"md\" or \"html\", exporting
+of those blocks falls back to the respective exporters."
+  (cond
+   ((string= (org-element-property :type export-block) "HUGO")
+    (org-remove-indentation (org-element-property :value export-block)))
+   ;; Also include Markdown and HTML export blocks.
+   ;; ox-md handles HTML export blocks too.
+   (t
+    (org-export-with-backend 'md export-block nil nil))))
 
 ;;;; Headline
 (defun org-hugo-headline (headline contents info)

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

@@ -2657,15 +2657,62 @@ 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:
+* Export snippets and blocks
+** Export snippet                                            :export_snippet:
+*** Export snippet Hugo                                                :hugo:
 :PROPERTIES:
-:EXPORT_FILE_NAME: export_snippets_and_blocks
+:EXPORT_FILE_NAME: export_snippet_hugo
+:END:
+@@hugo:This will get exported **only for** Hugo exports, `verbatim`.@@
+
+@@newlines
+are not
+allowed@@
+
+If you want newlines, use *Export Blocks* instead.
+*** Export snippet Markdown                                        :markdown:
+:PROPERTIES:
+:EXPORT_FILE_NAME: export_snippet_markdown
+:END:
+@@md:This Markdown **Export Snippet** will also get exported for Hugo exports, `verbatim`.@@
+
+@@markdown:_This one too_@@
+- NOTE :: =ox-md.el= does not support *Export Snippets* as of writing
+          this <2017-12-08 Fri>. So even the =@@md:foo@@= and
+ =@@markdown:foo@@= snippets are handled by =ox-hugo=
+          directly.
+*** Export snippet HTML                                                :html:
+:PROPERTIES:
+:EXPORT_FILE_NAME: export_snippet_html
+:END:
+@@html:This HTML <b>Export Snippet</b> will also get exported for Hugo exports, <code>verbatim</code>.@@
+** Export block                                                :export_block:
+*** Export block Hugo                                                  :hugo:
+:PROPERTIES:
+:EXPORT_FILE_NAME: export_block_hugo
 :END:
-** Export snippet
-@@hugo:This will get exported only for Hugo exports, `verbatim`.@@
-** Export block
 #+BEGIN_EXPORT hugo
-and **this too**.. `verbatim`.
+This will get exported **only for** Hugo exports, `verbatim`.
+#+END_EXPORT
+*** Export block Markdown                                          :markdown:
+:PROPERTIES:
+:EXPORT_FILE_NAME: export_block_markdown
+:END:
+#+BEGIN_EXPORT markdown
+This Markdown **Export Block** will also get exported for Hugo exports,
+`verbatim` ..
+#+END_EXPORT
+
+#+BEGIN_EXPORT md
+and **this too**.
+#+END_EXPORT
+*** Export block HTML                                                  :html:
+:PROPERTIES:
+:EXPORT_FILE_NAME: export_block_html
+:END:
+#+BEGIN_EXPORT html
+This HTML <b>Export Block</b>  will also get exported for Hugo exports,
+<code>verbatim</code>.
 #+END_EXPORT
 * Miscellaneous Front Matter                                   :front_matter:
 ** Hugo Aliases                                                     :aliases:

test/site/content/posts/export_block_html.md

@@ -0,0 +1,8 @@
++++
+title = "Export block HTML"
+tags = ["export-block", "html"]
+draft = false
++++
+
+This HTML <b>Export Block</b>  will also get exported for Hugo exports,
+<code>verbatim</code>.

test/site/content/posts/export_block_hugo.md

@@ -0,0 +1,7 @@
++++
+title = "Export block Hugo"
+tags = ["export-block", "hugo"]
+draft = false
++++
+
+This will get exported **only for** Hugo exports, `verbatim`.

test/site/content/posts/export_block_markdown.md

@@ -0,0 +1,10 @@
++++
+title = "Export block Markdown"
+tags = ["export-block", "markdown"]
+draft = false
++++
+
+This Markdown **Export Block** will also get exported for Hugo exports,
+`verbatim` ..
+
+and **this too**.

test/site/content/posts/export_snippet_html.md

@@ -0,0 +1,7 @@
++++
+title = "Export snippet HTML"
+tags = ["export-snippet", "html"]
+draft = false
++++
+
+This HTML <b>Export Snippet</b> will also get exported for Hugo exports, <code>verbatim</code>.

test/site/content/posts/export_snippet_hugo.md

@@ -0,0 +1,13 @@
++++
+title = "Export snippet Hugo"
+tags = ["export-snippet", "hugo"]
+draft = false
++++
+
+This will get exported **only for** Hugo exports, `verbatim`.
+
+@@newlines
+are not
+allowed@@
+
+If you want newlines, use **Export Blocks** instead.

test/site/content/posts/export_snippet_markdown.md

@@ -0,0 +1,14 @@
++++
+title = "Export snippet Markdown"
+tags = ["export-snippet", "markdown"]
+draft = false
++++
+
+This Markdown **Export Snippet** will also get exported for Hugo exports, `verbatim`.
+
+_This one too_
+
+-   **NOTE:** `ox-md.el` does not support **Export Snippets** as of writing
+    this <span class="timestamp-wrapper"><span class="timestamp">&lt;2017-12-08 Fri&gt;</span></span>. So even the `@@md:foo@@` and
+    `@@markdown:foo@@` snippets are handled by `ox-hugo`
+    directly.

test/site/content/posts/export_snippets_and_blocks.md

@@ -1,14 +0,0 @@
-+++
-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`.