output file suffix.

have a fillval attribute, allowing column-specific fill value to be set - used
by binariseCategorical.

column data gets formatted correctly

refactorings to remove assumptions of single-column index

on import - not sure why it was happening here? Perhaps it was once upon a
time

--num_jobs is set to 1.

a sequence of new column names

are no data columns to be exported.

import function.