Add SICP exercise 3.39
Add SICP exercise 3.40
Add SICP exercise 3.41
Add SICP exercise 3.42
Take interleave cases into consideration in ex3.40
Add SICP exercise 3.44
Add SICP exercise 3.45
Add SICP exercise 3.46
Add SICP exercise 3.47
Add SICP exercise 3.48
Add SICP exercise 3.49