First exercise for the second chapter.
Third exercise for the second chapter.
Fourth exercise for the second chapter.
Fifth exercise for the second chapter.
Use ^ over ** to express the power function.

See http://www.haskell.org/haskellwiki/Power_function
Improve the answer for the third exercise.
Merge pull request #2 from laurocaetano/ch-02

Exercises for the second chapter.