add some ASP in gaming references

[tortinator]

ADD

@inproceedings{SMSOW18,
  author    = {Adam Summerville and
               Chris Martens and
               Ben Samuel and
               Joseph C. Osborn and
               Noah Wardrip{-}Fruin and
               Michael Mateas},
  title     = {Gemini: Bidirectional Generation and Analysis of Games via {ASP}},
  booktitle = {Proceedings of the Fourteenth {AAAI} Conference on Artificial Intelligence
               and Interactive Digital Entertainment, {AIIDE} 2018, November 13-17,
               2018, Edmonton, Alberta, Canada},
  pages     = {123--129},
  year      = {2018},
}

@article{Smith12,
  author    = {Adam M. Smith},
  title     = {Constrained Videogame Content Generation with Answer Set Programming},
  journal   = {TinyToCS},
  volume    = {1},
  year      = {2012},
}