tilable-img_0044.png:
  from http://opengameart.org/node/9703
  by http://opengameart.org/users/p0ss
  license: GPL 2.0 or above

brushwalker437.png:
  from http://opengameart.org/node/10593
  by http://opengameart.org/users/qubodup
  license: public domain

large-stone-wall.png and stone_wall_4.png:
  from http://opengameart.org/content/wall-grass-rock-stone-wood-and-dirt-480
  by West
    submitted by http://opengameart.org/users/qubodup
  license: public domain

concrete:
  from http://opengameart.org/content/p0sss-texture-pack-1
  by http://opengameart.org/users/p0ss
  license: CC-BY 3.0, GPL 3.0 or above