Splitting a long file using the signals of different element, instead of 'total_counts'

[sunwillrise]

Hello. Thank you for implementing #16 !

I used the latools.preprocessing.split.long_file() to split my data. In my case, using total_counts didn't work well, so changed to the code a bit to use different signals from different elements. Originally, it is

# autorange
bkg, sig, trn, _ = autorange(dat['Time'], dat['total_counts'], **autorange_args)

but I wanted to use the signals of Fe. So I did

# autorange
bkg, sig, trn, _ = autorange(dat['Time'], dat['rawdata']['57Fe'], **autorange_args)

Hope this helps someone!