- testing DZI::Files: files are really written, all of them
- A4: draw a zigzag line over the pages to indicate the sequence
- A4: accept a document linear/exponential parameter, linear generates 1x1, 2x2, 3x3, 4x4, ..

- DZI: stretch parameter != 1? then do a more intelligent crop:
    1) crop larger than tile necessary
    2) resize this (to avoid artefacts)
    3) crop again, at tile size

- add Graphics::DZI::cpio (if there were a streaming solution)
- add Graphics::DZI::tar (if there were a *working* streaming solution
- add Graphics::DZI::DAV
- tests must be improved over time
- add --overlay option to deepzoom