[prob_matrix] Restructure and Split (#484)

Co-authored-by: thomassargent30 <[email protected]>

Author: HumphreyYang

lectures/_toc.yml

@@ -15,6 +15,7 @@ parts:
   numbered: true 
   chapters:
   - file: prob_matrix
+  - file: stats_examples
   - file: lln_clt
   - file: prob_meaning
   - file: multi_hyper