Add match info to the protocol

New message proposal:

```
match {player A token} {player B token}
```

This will allow UABC to improve the displayed stats, as it will know when matches end.
Although for online play, it would be easier to maintain if the server sent the match stats to UABC directly.

The `match` message will appear in the log files, and it'll allow the analyse tab in the website to group games by match.