Add meloref to author system

private_includes/base/default_songinfo_style.ily

@@ -7,6 +7,7 @@
   poetAndComposerEqualPrefix = "Worte und Weise:"
   voicePrefix = "Stimme:"
   versePrefix = "Strophe:"
+  refPrefix = "Refrain:"
   translationAuthorPrefix = "Übersetzung:"
   translationPrefix = "Übersetzung:"
   pronunciationPrefix = "Aussprache:"
@@ -39,6 +40,7 @@
         (versePoetData '())
         (composerIds '())
         (verseComposerData '())
+        (refComposerIds '())
         (voiceComposerData '())
         (compositionIds '())
         (adaptionTextIds '())
@@ -48,6 +50,7 @@
         (year_text #f)
         (year_translation #f)
         (year_melody #f)
+        (year_melody_meloref #f)
         (year_composition #f)
         (year_adaption_text #f)
         (year_adaption_music #f)
@@ -60,12 +63,14 @@
         (adaptionTextPrefix "")
         (adaptionMusicPrefix "")
         (bridgePrefix "")
-        (interludePrefix ""))
+        (interludePrefix "")
+        (refPrefix ""))
       (if (and
             (equal? poetIds composerIds)
             (null? translatorIds)
             (null? versePoetData)
             (null? verseComposerData)
+            (null? refComposerIds)
             (null? voiceComposerData)
             (null? compositionIds)
             (null? adaptionTextIds)
@@ -104,6 +109,7 @@
                 (null? compositionIds)
                 (null? adaptionMusicIds)
                 (null? verseComposerData)
+                (null? refComposerIds)
                 (null? voiceComposerData)
                 (null? bridgeIds)
                 (null? interludeIds)) #f
@@ -116,6 +122,10 @@
                   year_melody
                 ) ", ")
                 (render-partial-contribution-group 'versePrefix verseComposerData)
+                (join-present (list
+                  (render-contribution-group refPrefix refComposerIds)
+                  year_melody_meloref
+                ) ", ")
                 (render-partial-contribution-group 'voicePrefix voiceComposerData)
                 (join-present (list
                   (render-contribution-group compositionPrefix compositionIds)