add chapter2.scm
Done with section 2.2
Done with section 2.3
format code
Exercise 3.1.2
Exercise 3.2.1
Exercise 3.3.1
Exercise 3.3.2
Exercise 3.3.3
Exercise 3.3.4
Exercise 3.3.5
Exercise 3.3.6
Exercise 4.1.1 and 4.1.2
Exercise 4.2.1
Exercise 4.2.2
Exercise 4.2.3
Exercise 4.3.1
Exercise 4.3.3
Exercise 4.4.1
Exercise 4.4.2