some imports
add optional fileName argument
always convert to float32 if out dtype is float64
get out of the way, print
use non_linear_unwarp_siemens if possible, and requested

added in the --hcp argument to avoid overloading filename.

It's possible that the two non_linear_unwarp methods could be merged in the future, but I didn't write either, and don't feel like fiddling with them. So here.