@mluessi I used `int` for consistency with `fit_point_cloud`, where it can be 0, 1 or 3. Also, in the future someone might want to add the option to use 3 parameters. The function is currently only used to do a fit using the 3 fiducial points, so estimating translation, rotation and 3 scaling parameters would be too much. 

@agramfort I added:
```
With 0, points are not scaled. With 1, 
        points are scaled by the same factor along all axes. 
```