Writes matrix /data frame to nifti files columnwise.
Each column of the matrix should correspond to the labels of a nifti file.
i.e. nrow of matrix = n of labels in labeledNifti
Niftis are written in parallel using parallel::parApply
labels2niftis(datamat, labeledNifti, prefix, verbose = TRUE,
n.cores = parallel::detectCores())
Matrix / Data Frame: Input
String: Path to labeled nifti file
String: File output prefix
Logical: If TRUE, print messages to output
Integer: Number of cores to use