Add Hopenhayn lecture (#173)

* Add a new section on macroeconomic models

* Add Hopenhayn lecture

* Add to toc

* fix error

* interchange order in toc

* apply suggestions

Author: kp992

lectures/_toc.yml

@@ -28,9 +28,13 @@ parts:
   - file: opt_invest
   - file: inventory_ssd
   - file: ifp_egm
+  - file: cake_eating_numerical
+- caption: Macroeconomic Models
+  numbered: true
+  chapters:
   - file: arellano
   - file: aiyagari_jax
-  - file: cake_eating_numerical
+  - file: hopenhayn
 - caption: Data and Empirics
   numbered: true
   chapters: