option to append to files in command-line tools
Joachim Klein has a scenario where he would like
ltlcross --save-bogus=FILENAME to append to FILENAME instead of overwriting it.
Appending would also make sense for
ltlcross --grind and for the planned
--output option (see #56 (closed)). Maybe also for
--csv (in this case we would not output the header).
Maybe we can have the convention that if
FILENAME starts with
>> it means we want to append to the file.