A superb bit of software that I use for all my C64 games.
One option I'd love to be added to the compress data is 'only clear un-used chars' or perhaps even the option to specify a character index to start from other than 0.
What I mean by that is often I'll have my A-Z, 0-9 and a few other common symbols in my set, in the correct place to be used programatically. If I want to retain those I can just draw them in an un-used part of the map.
But when I compress data, any currently un-used chars in between those sub-sets are deleted and now the symbols and numbers are in the wrong place. So it would be nice if un-used chars were just optionally cleared rather than deleted.