In order to make the class more generic, also handle more than 65535
frames (Number of Frames can be 2^32-1 max).

Also remember frame positions in sorting result since it is usually
accessed anyway and interesting for library users that otherwise call
the underlying method on FGInterface for all frames again.

The DummySorter does not provide frame positions to keep it as simple
as possible (i.e. keep  it "zero" cost).

Allow 2^32-1 frames as permitted in in DICOM (i.e. use Uint32 instead
of  Uint16) for frame number index.

Changed precision from Float32 to Float64 where applicable.

Added some documentation.

Switch to framesorter class

Make sure input data has been  initialized  by user before public
methods are called.

Made logging message more consistent.

Made code more readable.

When converting from ITK to DICOM, allow to use Label IDs as Segment
Numbers so that even if reading from various NRRD inputs, the Segments
in the DICOM file will still use the Label IDs from the NRRD files.

This is particularly helpful for testing since it allows a roundtrip test
from DICOM -> multiple NRRD files using potentially multiple segments
each -> back to DICOM. If no mapping to the Label IDs takes place, the
converter will use ascending Segment Numbers, so the order will depend
on the read order, which again usually depends on the order in the JSON
meta information.

This sorting behavior is disabled by default. It is available as
cli option (--sortByLabelID) which is handed to the library through the
Itk2DicomConverter::itkimage2dcmSegmentation() call.

Added missing test dependency.

Renamed feature from sortByLabel to useLabelIDAsSegmentNumber.
Added check for unique, monotonically increasing label IDs before
starting reassignment.
Added missing update of ReferencedFrameNumber.

…bers

Use labelIDs as segment numbers

The order in which the values for pixel spacing in ITK and DICOM are
stored is different. In DICOM the first value is the row spacing
(i.e. Y axis) while in ITK the first value is spacing along the X axis.

Reading asymmetric spacings from DICOM segmentations has already been
fixed in 46c6f0.

This commit fixes writing DICOM segmentation objects with asymmetric
spacings.

…xel_spacing

Fix order of pixel spacing converting ITK->DICOM.

aims to resolve #487

Re #487 thanks to @michaelonken!