Use a more elegant syntax to select diagrampages

patacrep/data/templates/songbook_model.yml

@@ -55,8 +55,14 @@ schema:
               value: "guitar"
             - type: //str
               value: "ukulele"
-            - type: //str
-              value: "guitar+ukulele"
+            - type: //arr
+              contents:
+                type: //any
+                of:
+                  - type: //str
+                    value: "guitar"
+                  - type: //str
+                    value: "ukulele"
         notation:
             type: //any
             of:

patacrep/templates.py

@@ -325,5 +325,7 @@ def iter_bookoptions(config):
         elif config['chords']['diagrampage'] == "all":
             yield 'diagrampage'
 
-        for instrument in config['chords']['instrument'].split("+"):
-            yield instrument
+        if isinstance(config['chords']['instrument'], str):
+            yield config['chords']['instrument']
+        else:
+            yield from config['chords']['instrument']