Add answer for first 3 exercises
Add answer to ex04
Refactor merge implementation

The initial implementation was complicated because I missed the detail
that both list are already sorted, so once one gets empty, the other can
be append entirely to the end
Add answer for exercise 5
Add answer to exercise 6
Add a different approach to pattern matching
Remove unnecessary pattern matching
Add another pattern matching for single element list
Fix take implementation with 0 case
Add a recursive version of and
Add the five steps to write recursive functions
Add power evaluation
Merge pull request #6 from fabioyamate/ch06

Chapter 6: Recursive Functions