…/doc …/log: .gz → .zst

[Adam Borowski <kilobyte@angband.pl>]

Meow!
Because of the trimming changelogs discussion, I just wondered whether
it'd be beneficial to switch compression from .gz to .zst (gzip to zstd).

Numbers I got from the desktop I sit at:

* du of a copy of /usr/share/doc
366692
* rm ! -name "*.gz"
194184
* decompress
656852
* repack as zstd
163340

31MB saving, decent but not world shattering.  Let's do so...?


But then, I looked at /var/log

* du
257612
* rm ! -name "*.gz"
53028
* decompress
471892
* repack as zstd
16360

Holy apt!  Now this is a find!  This box is a desktop thus doesn't produce
a lot of logs (just sbuild spam), but there's quite a few of my boxen where
logs get very bulky.

Thus: let's switch logrotate from gzip to zstd?  As changing the default
would upset scripts, let's do it at the same time as enabling dateext...


Meow!
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