Release 0.2.0: changelog, version reporting, push-to-deploy

- CHANGELOG.md following Keep a Changelog, covering 0.1.0 and 0.2.0
- server/version.js reads the version from package.json; /healthz returns it
  and the footer renders it, so a deployment always states what it is serving
- bump package.json 0.1.0 -> 0.2.0

README.md

@@ -74,6 +74,11 @@ ADMIN_PASSWORD=test PORT=3123 npm start &  BASE=http://localhost:3123 ADMIN_PASS
 
 Architecture and the reasoning behind it: [docs/ARCHITECTURE.md](docs/ARCHITECTURE.md). Endpoints: [docs/API.md](docs/API.md).
 
+## Releases
+
+Versions and what changed in each: [CHANGELOG.md](CHANGELOG.md). The running
+version is in the page footer and at `GET /healthz`.
+
 ## License
 
 MIT. See [LICENSE](LICENSE).