message: Add to/from_json for LinearSpace2f
  used by texture transformation
diff: @@ -293,6 +293,18 @@ inline void from_json(const JSON &j, vec4f &v)
  j.at(3).get_to(v.w);
  }
  +inline void to_json(JSON &j, const LinearSpace2f &ls)
  +{
  + j = JSON{{"x", ls.vx}, {"y", ls.vy}};
  +}
  +
  +inline void from_json(const JSON &j, LinearSpace2f &ls)
  +{
  + j.at("x").get_to(ls.vx);
  + j.at("y").get_to(ls.vy);
  +}
  +
  +
  inline void to_json(JSON &j, const LinearSpace3f &ls)
  {
  j = JSON{{"x", ls.vx}, {"y", ls.vy}, {"z", ls.vz}};
  