extract meta data from lilypond compilation

public_includes/layout_bottom.ily

@@ -72,6 +72,8 @@ TEXT = \markuplist {
     (if paper (set! $defaultpaper paper))
   )
 
+  ;(ly:warning (format #f "~a" (bookpart->header-alist HEADER)))
+
   ;; ChordPro export: Store filename and extract metadata from basicSongInfo FIRST
   (when (and (defined? 'chordpro-export-enabled) chordpro-export-enabled)
     ;; Use ly:parser-output-name which returns the output basename