Use chapters for digital toc

* introduce \songsChapter and \markuppage
* have nested chapters in PDF toc

private_includes/book/toc_include.ily

@@ -366,7 +366,7 @@ headerToTOC = #(define-music-function (parser location header label) (ly:book? s
     (let ((song-lines (map (lambda (song)
             (let* ((filename (symbol->string (car song)))
                    (songvars (cdr song))
-                   (page-number (number->string (assoc-get (assq-ref songvars 'label) labelPageTable)))
+                   (page-number (assoc-get (assq-ref songvars 'label) labelPageTable))
                    (extractedheadervars (extract-and-check-vars-from-header (assq-ref songvars 'header)
                       '(title starttext alttitle categorytitle categories authors year_text year_melody year_translation year_composition year_adaption infotext translation pronunciation copyright source)))
                    (headervar-or-empty (lambda (varsym)
@@ -413,7 +413,7 @@ headerToTOC = #(define-music-function (parser location header label) (ly:book? s
                   (format-info-paragraphs (headervar-or-empty 'translation))
                   (format-info-paragraphs (headervar-or-empty 'pronunciation))
               ))))
-            (alist-delete 'imagePage (alist-delete 'emptyPage song-list)))))
+            (alist-delete 'markupPage (alist-delete 'imagePage (alist-delete 'emptyPage song-list))))))
     (call-with-output-file "toc.csv"
       (lambda (port)
        (csv-write (cons '(
@@ -443,6 +443,6 @@ headerToTOC = #(define-music-function (parser location header label) (ly:book? s
   ; we use a delayed stencil to have all the page references available
   (ly:make-stencil
     `(delay-stencil-evaluation
-      ,(delay (let* ((table (ly:output-def-lookup layout 'label-absolute-page-table)))
+      ,(delay (let* ((table (ly:output-def-lookup layout 'label-page-string-table)))
         (generate-toc-csv (if (list? table) table '()))
         empty-stencil)))))