Add Exercises from Chapters 2 and 3.
Add Exercise 6.13.
Fix typo in Exercise 6.13.
Simplify formulation and change from print() to assert()
Add Exercise 6.14.
Add Exercise 5.1.
Add Exercises from Problem Set 7.
Add Exercise 8.1.
Add Exercise 8.2.
Add Exercise 8.3.
Add Exercises 8.4, 8.5.
Add Exercise 8.6.
Add Exercise 8.7.
Add Exercise 8.8.
Add Exercise 8.9.
Add Exercise 8.10.
Add Exercise 8.11.
Add Exercise 8.12.
Add Exercise 8.13.
Add Exercise 8.14.