added book mode MVP

test/simple/book.yaml

@@ -0,0 +1,26 @@
+book:
+  - fields: 
+    - name 
+    - id
+    - goal
+    - content
+    - form-of-instruction 
+    - prerequisites 
+    - media-of-instruction 
+    - author-of-indenture 
+    - used-in 
+    - workload 
+    - credits
+    - form-of-exam 
+    - term
+    - frequency 
+    - duration 
+    - kind
+    - remarks
+  - sections:
+    - text:
+        de: "## Pflichtbereich {.unnumbered}"
+        en: "## compulsory courses {.unnumbered}"
+    - modules: 
+        - mod.cg.yaml
+