* Making more unix-like - transformed data is now output to stdout (instead of
to a file); user may redirect this to a file if they so wish. Major version
incremented since this is not backwards-compatible.
* Separation of concerns - offset_subtitles no longer concerned with outputting
of data - it yields line-by-line & main function does the printing.
* Adding tests & test data.
* Small pep-8 tidying.
* Updated copyright year.