ver-chk: tests, docs, fix -j0 jank

docs/examples/docker/basic-docker-compose/copyparty.conf

@@ -22,6 +22,12 @@
   # stats, nos-dup   # enable the prometheus endpoint, but disable the dupes counter (too slow)
   # no-robots, force-js  # make it harder for search engines to read your server
 
+  # enable version-checking by uncommenting one of the vc-url lines below;
+  # shows a warning-banner in the controlpanel if your version has a known vulnerability
+  #vc-url: https://api.github.com/repos/9001/copyparty/security-advisories?per_page=9
+  #vc-url: https://api.copyparty.eu/advisories
+  vc-exit  # panic and shutdown instead of just showing the warning
+
 
 [accounts]
   ed: wark  # username: password

docs/versus.md

@@ -319,7 +319,7 @@ symbol legend,
 | speed throttle          |   | █ | █ |   |   | █ |   |   | █ |   |   | █ |   |
 | anti-bruteforce         | █ | █ | █ | █ | █ |   |   |   | • |   |   | █ | • |
 | dyndns updater          |   | █ | █ |   |   |   |   |   |   |   |   |   |   |
-| self-updater            |   |   | █ |   |   |   |   |   |   |   |   |   | █ |
+| self-updater            | ╱ |   | █ |   |   |   |   |   |   |   |   |   | █ |
 | log rotation            | █ |   | █ | █ | █ |   |   | • | █ |   |   | █ | • |
 | upload tracking / log   | █ | █ | • | █ | █ |   |   | █ | █ |   |   | ╱ | █ |
 | prometheus metrics      | █ |   |   | █ |   |   |   |   |   |   |   | █ |   |
@@ -343,6 +343,7 @@ symbol legend,
   * can hot-reload config files (with just a few exceptions)
   * can set per-folder permissions if that folder is made into a separate volume, so there is configuration overhead
   * `index.html` on its own does not prevent directory listing, but permission `h` (instead of `r`) enforces index.html to be returned instead of folder contents
+  * [update-checker](https://github.com/9001/copyparty/#update-checker) can check if the current version has a known vulnerability and immediately exit/shutdown, but automatic self-updating is **not** available
   * [event hooks](https://github.com/9001/copyparty/tree/hovudstraum/bin/hooks) ([discord](https://user-images.githubusercontent.com/241032/215304439-1c1cb3c8-ec6f-4c17-9f27-81f969b1811a.png), [desktop](https://user-images.githubusercontent.com/241032/215335767-9c91ed24-d36e-4b6b-9766-fb95d12d163f.png)) inspired by filebrowser, as well as the more complex [media parser](https://github.com/9001/copyparty/tree/hovudstraum/bin/mtag) alternative
   * upload history can be visualized using [partyjournal](https://github.com/9001/copyparty/blob/hovudstraum/bin/partyjournal.py)
 * `k`/filegator remarks: