List available variants for a game family. Each variant can be passed to play_create_game. Variants with flags (e.g. +random) can be requested as "slug+flag".

Game family (chess, draughts, go, reversi, shogi, xiangqi, mancala, morris, hex, landlords-game, backgammon, standard-52, bavarian-32, flower-48, double-six-dominoes, mahjong, standard-dice, agon, asalto, chaupar, dou-shou-qi, fanorona, halma, nyout, pachisi, royal-ur, senet, stern-halma, surakarta, tafl)