The function `imcrop_tosquare` in session-0 has a minor problem

```python
...
            crop = img[max(0, extra // 2 + 1):min(-1, -(extra // 2)), :]
...
```
The result will not be a square when extra is 1.
For example, the ```crop``` is ```img[1:-1, :]``` when ```extra``` is 1.

It should be:
```python
...
            crop = img[extra // 2:-(extra // 2) - 1, :]
...
```