extract meta data from lilypond compilation

* write that as yaml file next to the other outputs
* extract lyrics
* makes chordpro export work in songbooks
* more metadata for chordpro export

private_includes/base/verses_with_chords.ily

@@ -182,7 +182,19 @@
      ((if reverses fold fold-right) (lambda (element filled-list)
               (cons element (if (null? filled-list) '() (cons markup-between filled-list))))
         '() elements))
-   (let* ((column-item-count (ceiling (/ (length versegroup) verse-cols)))
+   ;; Dokumentposition fuer den ChordPro-/Data-Collector: jede Gruppe nimmt
+   ;; sich eine Sequenznummer, jeder Vers traegt seine Position innerhalb
+   ;; der Gruppe in den Props -- die Spalten-Verteilung unten verschraenkt
+   ;; sonst die Interpretationsreihenfolge.
+   (set! chordpro-doc-seq-counter (1+ chordpro-doc-seq-counter))
+   (let* ((doc-seq chordpro-doc-seq-counter)
+          (versegroup (index-map
+                       (lambda (index item)
+                         (make-override-markup
+                          (cons 'chordpro-doc-order (cons doc-seq index))
+                          item))
+                       versegroup))
+          (column-item-count (ceiling (/ (length versegroup) verse-cols)))
           (column-data (make-list verse-cols)))
     (let columnize-list ((index 0) (items versegroup))
       (if (not (null? items))
@@ -341,6 +353,20 @@ Chord_lyrics_spacing_engraver =
                  (transposition (cons #f #f))
                  (verselayout generalLayout))
   "Vers mit Akkorden"
+  ;; Dem ChordPro-Collector sagen, zu welchem Lied dieser Vers gehoert
+  ;; (Buch: songfilename aus den Props via \setsongfilename; Einzellied:
+  ;; Fallback-Key aus layout_bottom). Die Score-Interpretation darunter
+  ;; laeuft synchron, der Engraver liest den Key in initialize. Die Props
+  ;; braucht er zum Aufloesen von Markup-Silben (tags-to-keep).
+  (set! chordpro-active-song-key (chordpro-resolve-song-key props))
+  (set! chordpro-active-props props)
+  ;; Dokumentposition: von \group-verses gestempelt; ausserhalb einer
+  ;; Gruppe nimmt sich der Vers selbst eine Sequenznummer.
+  (set! chordpro-active-doc-order
+    (or (chain-assoc-get 'chordpro-doc-order props #f)
+        (begin
+          (set! chordpro-doc-seq-counter (1+ chordpro-doc-seq-counter))
+          (cons chordpro-doc-seq-counter 0))))
   (interpret-markup layout props
     #{
       \markup {