Make savegames robust without needing version

[ioan-chera]

I think a way to make saves more robust and perhaps even forget about versioning is to store them with named fields instead of purely sequential. Kinda like JSON but maybe simplified to be quickly readable and writable as binary without all the silly syntactic baggage. This way when loading you search for the fields by string, leaving default if not found, and there’ll be no problem of the wrong value getting into the wrong field and crashing. If the save file gets too big, we can use zlib to compress it. Care must be taken when we refactor the code, because we shouldn’t rename the field save names.