Add player.currentbet to _get_current_state

[BigBadBurrow]

I think it's useful information to have the player.currentbet available on player_infos:

      player_features = [
        int(player.emptyplayer),
        int(player.get_seat()),
        int(player.stack),
        int(player.playing_hand),
        int(player.handrank),
        int(player.playedthisround),
        int(player.betting),
        int(player.isallin),
        int(player.lastsidepot),
        int(player.currentbet),
      ]

[BigBadBurrow]

Suggested an improvement to this here