Fix syncthing process reparenting with runit

When you: `sudo sv down /etc/service/syncthing/` the `TERM` signal
isn't propogated or trapped, so syncthing is orphaned and adopted by
init (PID 1).

- Changed call to `chpst` to `exec`
- Moved logging to `log/run` per `runsv` standard

etc/linux-runit/run

@@ -4,5 +4,6 @@ export USERNAME=jb
 export HOME="/home/$USERNAME"
 export SYNCTHING="$HOME/bin/syncthing"
 
-chpst -u "$USERNAME" "$SYNCTHING" -logflags 0 2>&1 | logger -t syncthing
+exec 2>&1
+exec chpst -u "$USERNAME" "$SYNCTHING" -logflags 0