For consistency, make the audio front-matter a list too

.. like the videos and images front-matter.

ox-hugo.el

@@ -789,7 +789,7 @@ newer."
                    ;; aliases
                    (:hugo-aliases "HUGO_ALIASES" nil nil space)
                    ;; audio
-                   (:hugo-audio "HUGO_AUDIO" nil nil)
+                   (:hugo-audio "HUGO_AUDIO" nil nil newline)
                    ;; date
                    ;; "date" is parsed from the Org #+date or subtree property EXPORT_HUGO_DATE
                    (:date "DATE" nil nil)
@@ -3107,7 +3107,7 @@ INFO is a plist used as a communication channel."
          (data `(;; The order of the elements below will be the order in which the front-matter
                  ;; variables will be ordered.
                  (title . ,(org-hugo--sanitize-title info))
-                 (audio . ,(plist-get info :hugo-audio))
+                 (audio . ,(org-hugo--delim-str-to-list (plist-get info :hugo-audio)))
                  (author . ,author-list)
                  (description . ,description)
                  (date . ,(org-hugo--format-date :date info))

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

@@ -5619,11 +5619,20 @@ quotes.
 If a video path has spaces in it, wrap the whole path in double
 quotes.
 ** Audio                                                              :audio:
+*** Single audio file                                                :single:
 :PROPERTIES:
-:EXPORT_FILE_NAME: audio-front-matter
-:EXPORT_HUGO_AUDIO: "audio path with space.mp3"
+:EXPORT_FILE_NAME: audio-single
+:EXPORT_HUGO_AUDIOS: "audio path with space.mp3"
 :END:
-If the audio path has spaces in it, wrap the whole path in double
+If a audio path has spaces in it, wrap the whole path in double
+quotes.
+*** Multiple audio files                                           :multiple:
+:PROPERTIES:
+:EXPORT_FILE_NAME: audio-multiple
+:EXPORT_HUGO_AUDIOS: "audio foo.mp3"
+:EXPORT_HUGO_AUDIOS+: bar.wav
+:END:
+If a audio path has spaces in it, wrap the whole path in double
 quotes.
 ** Series                                                            :series:
 *** Single series                                                    :single:

test/site/content/posts/audio-front-matter.md

@@ -1,9 +0,0 @@
-+++
-title = "Audio"
-audio = "audio path with space.mp3"
-tags = ["front-matter", "audio"]
-draft = false
-+++
-
-If the audio path has spaces in it, wrap the whole path in double
-quotes.

test/site/content/posts/audio-multiple.md

@@ -0,0 +1,8 @@
++++
+title = "Multiple audio files"
+tags = ["front-matter", "audio", "multiple"]
+draft = false
++++
+
+If a audio path has spaces in it, wrap the whole path in double
+quotes.

test/site/content/posts/audio-single.md

@@ -0,0 +1,8 @@
++++
+title = "Single audio file"
+tags = ["front-matter", "audio", "single"]
+draft = false
++++
+
+If a audio path has spaces in it, wrap the whole path in double
+quotes.