The function `die` was redundantly implemented in various files.
Move the function into .local/bin/helpers.sh and source that where
previously implemented.
Also prepend the program's name to the message and always terminate the
message with a newline. The newline was previously needed for a small
but unnecessary hack that prevented the need of the `[ -z "$1" ]` test.
Refactor the script to match my coding style more and update the
comments.
When checking the filenames for non-ASCII characters, check also
renaming of files instead of only additions.
