Chapter 7: Higher-order functions

@carlosgaldino and @laurocaetano Finally I finished the chapter 7 exercises.

The exercise 7 took me some time because it wasn't work as I expected. But, once I did the evaluation steps it  was easy to fix it.

The exercises 8 and 9, not sure if it was the best solution.
This parity thing confused me. The `int2bin` function generates the bin number from left to right, which is the inverse of the traditional representation.

```haskell
make8 . int2bin $ 8 
> [0,0,0,1,0,0,0,0]
```
the common representation is the inverse: `0000 1000`.

But I think that in both places would be ok, at least it doesn't mention where the bit should go.