add more interp choices
added more interpolation choices
users can now choose from [nearestneighbour (or nn), trilinear, spline, sinc (default)]
updated option parsing
the first 4 args are positional, while the remaining options can be set by users in any order (that behaviour is different from before, but still backwards compatible).
updated usage text
Usage: applyxfm4D <input volume> <ref volume> <output volume> <transformation matrix file/dir>
--interp, -interp [nearestneighbour (or nn), trilinear, spline, sinc (default)]
--singlematrix, -singlematrix (flag option, do not provide an argument)
--fourdigit, -fourdigit (flag option, do not provide an argument)
--userprefix, -userprefix <prefix>
other stuff
3D hidden option can now be any of [-3d, --3d, -3D, --3D]