Void function returing according to the documentation a value

In the files `aopt.h` and `aopt.cpp` we see as documentation of the function `void aopt_exit(AOPT_OBJECT *aopt_obj):`:
```
* @return @a none
```
Though the function has no return value but here there is a bit of a suggestion that the entity `none` (whatever that might be) is returned.

I think it would be better to remove the `@return` for the `void` function, though it is a matter of taste.