Switch from xz to zst compression for official artifacts

I've always preferred ZSTD do XZ anyway, but the default Ubuntu runner
GitHub Actions used to use was so old that it did not have
a sufficiently new autotools release to have ZSTD support. Hence XZ was
always a compromise to get better compression without compatibility
problems. Times have changed, the upstream `xz-utils` project has been
backdoored, and ZSTD is available in Ubuntu LTS releases so we don't
have a problem auto-generating releases any more.

As-yet no evidence has surfaced that XZ compressed artifacts are
compromised, but since there are no blockers anyway switching seems like
a good plan to me.

Author: alerque

.github/workflows/release.yml

@@ -41,8 +41,8 @@ jobs:
           prerelease: ${{ env.PRERELEASE }}
           body_path: changelog-HEAD
           files: |
+            vcsh-${{ env.VERSION }}.tar.zst
             vcsh-${{ env.VERSION }}.zip
-            vcsh-${{ env.VERSION }}.tar.xz
 
   deploy-standalone:
     runs-on: ubuntu-latest

configure.ac

@@ -2,7 +2,7 @@ AC_PREREQ([2.69])
 AC_INIT([vcsh], [m4_esyscmd(build-aux/git-version-gen .tarball-version)])
 AC_CONFIG_AUX_DIR([build-aux])
 AC_CONFIG_MACRO_DIR([build-aux])
-AM_INIT_AUTOMAKE([foreign tar-pax dist-xz dist-zip no-dist-gzip color-tests])
+AM_INIT_AUTOMAKE([foreign tar-pax dist-zstd dist-zip no-dist-gzip color-tests])
 AM_SILENT_RULES([yes])
 
 AM_CONDITIONAL([IS_SDIST],

doc/INSTALL.md

@@ -81,7 +81,7 @@ $ pkg install vcsh
 
 First you’ll want a copy of the source code.
 The easiest to use place to get this is the [latest release](https://github.com/RichiH/vcsh/releases/latest) posted on GitHub.
-The souree distribution will have a name such as `vcsh-2.0.0.tar.xz`.
+The souree distribution will have a name such as `vcsh-2.0.0.tar.zst`.
 Note under each release GitHub also show two “Source code” links that will download a snapshot of the repository; this is **not** the file you want (unless you want to jump through extra hoops).
 The official source release packages with the release version in the file names are the ones you want.