one of the biggest issues with borg < 1.0 was that it had a default target chunk
size of 64kiB, thus it created a lot of chunks, a huge chunk management overhead
(high RAM and disk usage).
outdated - it just showed different levels of zlib compression,
but not we additionally have "lzma", "lz4" and "none" compression.
the "usage" and "internals" docs give some hints about them, too.
