Release 2.3.0.0202: version-tagged images, changelog

- Drone: an image-tags step writes .tags (latest, commit SHA, changelog
  version) for the master publish, so each release can be pulled and
  rolled back by version. The master publish step no longer hardcodes tags.
- Version 2.2.0.0201 -> 2.3.0.0202 in xteve.go and changelog-beta.md, with
  a changelog entry covering the improvements branch.
- README / README-DEV describe the version tag.

.drone.yml

@@ -51,6 +51,22 @@ steps:
       event:
         - pull_request
 
+  # plugins/docker reads its tag list from a .tags file when no "tags"
+  # setting is given. Master images get latest, the commit SHA and the
+  # release version from changelog-beta.md, so a release can be pulled by name.
+  - name: image-tags
+    image: cache.coadcorp.com/library/golang:1.27.1
+    commands:
+      - XTEVE_VERSION="$(grep -m1 '^#### ' changelog-beta.md | cut -d' ' -f2 | sed 's/-beta$//')"
+      - test -n "$XTEVE_VERSION"
+      - printf '%s' "latest,${DRONE_COMMIT_SHA},$XTEVE_VERSION" > .tags
+      - cat .tags
+    when:
+      event:
+        - push
+      branch:
+        - master
+
   - name: docker-publish
     image: plugins/docker
     environment:
@@ -63,9 +79,6 @@ steps:
       username: nathan
       password:
         from_secret: registry_password
-      tags:
-        - latest
-        - ${DRONE_COMMIT_SHA}
       build_args:
         - TARGETOS=linux
         - TARGETARCH=amd64