#21 scanio add an option to scale scans

[Joschka van der Lucht]

In addition to the existing filter options, add an option to scale the scans while reading them. Scaling is currently hardcoded in the respective scanio readers and it would be nice if the scale could be set via the command line. While one is at it, one could also think about passing a 4x4 matrix which would not only allow scaling but also rotation and translation.