DicomImage

class.

might be in memory.

doc tweaks.

related code in atlas classes

has no effect when downsampling to a new shape where voxel centres are
aligned.

for us when a new nibabel image is created from an array+existing header

the former aligns on the centre of voxel (0, 0, 0), whereas the latter aligns
on the corner.

adjusted resample method to force float output (although this might change).

property. Also added scaledVoxToVoxMat

from fsleyes OverlayInfoPanel)

featdesign.loadDesignMat function

gzip image.

written to, the old coverages are not discarded - rather, the new data range
is calculated on the union of the old coverage and the write slice, across all
volumes.