Export player stats in json format

A few mentions
https://github.com/ceular/devotion/blob/44391031bcfd705e3015ee739a823c389044ad90/ratoa_gamecode/code/game/g_main.c#L3431

https://github.com/ceular/devotion/blob/abe0b7eee80a0f61dceb128fb528f759bb40e869/ratoa_gamecode/code/game/g_stats.c