Wrong value returned from xor function in fandango module

In some cases `functional.xor`  function returns boolean instead of argument.
``` python
from fandango import functional
functional.xor(0, 2)
```
returns `2` but:

``` python
from fandango import functional
functional.xor(2, 0)
```
returns `True`

``` python
from fandango import functional
functional.xor(2, 2)
```
returns `False`