Add SICP exercise 4.22
Add SICP exercise 4.23
Add empty ex4.24 for later complete
Add SICP exercise 4.25
Add SICP exercise 4.26
Make evaluator runnable, during prepare ex4.27
Make evaluator lazy, prepare ex4.27
Move lazy evaluator to individual file name
Add SICP exercise 4.27
Add SICP exercise 4.28
Add SICP exercise 4.29
Add SICP exercise 4.30