Replace Gzip zcat with zstdcat

[autape]

zcat works only with gzip files. I'm reminded of this on systems with 
defaults.

As far as I know, zstdcat is a drop-in replacement, works with gzip, xz, 
zstd, and more. In some sense, both `provides` zcat.

Pacman packages are zstd, I would assume it is as oblivious on the 
system as is gzip.

GZIP(1):
> On some systems, zcat may be installed as gzcat to preserve the 
original link to compress.

This is a petition for a better default: to install Gzip's as gzcat, and 
symlink zcat to zstdcat. Not exactly sure, where it should go to reach 
packaging.