Remove the large 5D nii file that was previously used for testing.
Create two new pieces of test data, both manufactured:
One that has the same header as the original data (ie, same dimensions) but is much smaller because all voxel intensities are 0 and it is gz compressed. The original 5D test was adapted to match the pattern for tests against other compressed datasets in the repo but was minimally modified otherwise.
One that has random values written to the voxel data, is not compressed, but is very small. See test for details.
NB this removed the test data from the repo at the point the PR was merged so should help the original issue (#11) where downloads from npm are large (once merged + published). This does nothing to remove the large testing data from the git object store, that should be considered a separate issue IMO.
Fixes #11
gzcompressed. The original 5D test was adapted to match the pattern for tests against other compressed datasets in the repo but was minimally modified otherwise.