This process compresses (gzip) all the fits level-0 files produced.
Init
initialises program global variables and decodes the command line arguments.
interactive processing
runs if command line arguments other than the pending flags (-p or --pending) are detected.
It sets the plan's start and end dates and the start and end times.
cron processing
runs if there are no command line arguments which is the case when started by cron.
If the pending flags (-p or --pending) are given then this indicates that cron has started the program and has found an entry in the tracking file; the tracking file records the dates and times of previous attempts at reformating which have failed for some reason (incomplete hk coverage for example).
Errors in processing lead to the pipeline exiting early through the
Pipeline exit
process with error code of ? and error message ?.
