Add exercies of chapter 02.

/cc @fabioyamate, @laurocaetano
I see what you mean, but look:

```
Prelude> 10 `div` length [1, 2]
5
```

And then take a look at the difference on the book:

![](http://img.carlosgaldino.com/programming_in_haskell.pdf_page_27_of_184_2014-07-08_16-45-02_2014-07-08_16-45-14.png)

and the exercise example:

![](http://img.carlosgaldino.com/programming_in_haskell.pdf_page_29_of_184_2014-07-08_16-44-32_2014-07-08_16-44-49.png)