MAINT: Adjust _toc.yml to adopt jb-book format structure

lectures/_toc.yml

@@ -1,45 +1,50 @@
-format: jb-article
+format: jb-book
 root: index
-sections:
-- file: introduction/index
-  sections:
-  - file: introduction/overview
-  - file: introduction/getting_started
-  - file: introduction/cloud_setup
-  - file: introduction/local_install
-  - file: introduction/troubleshooting
-- file: python_fundamentals/index
-  sections:
-  - file: python_fundamentals/basics
-  - file: python_fundamentals/collections
-  - file: python_fundamentals/control_flow
-  - file: python_fundamentals/functions
-- file: scientific/index
-  sections:
-  - file: scientific/numpy_arrays
-  - file: scientific/plotting
-  - file: scientific/applied_linalg
-  - file: scientific/randomness
-  - file: scientific/optimization
-- file: pandas/index
-  sections:
-  - file: pandas/intro
-  - file: pandas/basics
-  - file: pandas/the_index
-  - file: pandas/storage_formats
-  - file: pandas/data_clean
-  - file: pandas/reshape
-  - file: pandas/merge
-  - file: pandas/groupby
-  - file: pandas/timeseries
-  - file: pandas/matplotlib
-- file: applications/index
-  sections:
-  - file: applications/visualization_rules
-  - file: applications/regression
-  - file: applications/recidivism
-  - file: applications/maps
-  - file: applications/classification
-  - file: applications/working_with_text
-  - file: applications/ml_in_economics
-  - file: applications/heterogeneity
+parts:
+- caption: Introduction
+  chapters:
+    - file: introduction/index
+    - file: introduction/overview
+    - file: introduction/getting_started
+    - file: introduction/cloud_setup
+    - file: introduction/local_install
+    - file: introduction/troubleshooting
+- caption: Python Fundamentals
+  chapters:
+    - file: python_fundamentals/index
+    - file: python_fundamentals/basics
+    - file: python_fundamentals/collections
+    - file: python_fundamentals/control_flow
+    - file: python_fundamentals/functions
+- caption: Scientific Computing
+  chapters:
+    - file: scientific/index
+    - file: scientific/numpy_arrays
+    - file: scientific/plotting
+    - file: scientific/applied_linalg
+    - file: scientific/randomness
+    - file: scientific/optimization
+- caption: Pandas
+  chapters:
+    - file: pandas/index
+    - file: pandas/intro
+    - file: pandas/basics
+    - file: pandas/the_index
+    - file: pandas/storage_formats
+    - file: pandas/data_clean
+    - file: pandas/reshape
+    - file: pandas/merge
+    - file: pandas/groupby
+    - file: pandas/timeseries
+    - file: pandas/matplotlib
+- caption: Applications
+  chapters:
+    - file: applications/index
+    - file: applications/visualization_rules
+    - file: applications/regression
+    - file: applications/recidivism
+    - file: applications/maps
+    - file: applications/classification
+    - file: applications/working_with_text
+    - file: applications/ml_in_economics
+    - file: applications/heterogeneity