message: Assign texture when usemtl was part
  This requires the group name to always be set beforehand, which seems to be the
  case with all Moana obj files
diff: @@ -387,16 +387,29 @@ static void load_obj(
  surf->name() = std::string(group_name.begin(), group_name.length());
  + }
  + }
  + else if ( qi::phrase_parse(it, text.cend(), grammar.r_usemtl, qi::blank, mtl_name) )
  + {
  + // Material
  + std::string usemtl = mtl_name.to_string();
  + auto mit = materials.find(usemtl);
  + if (mit != materials.end())
  + {
  + surf->material() = mit->second;
  + }
  +
  + // Color texture
  std::string group = group_name.to_string();
  - auto it = textures.find(group);
  - if (it != textures.end())
  + auto tit = textures.find(group);
  + if (tit != textures.end())
  {
  - surf->add_texture(std::static_pointer_cast<sg::texture>(it->second));
  + surf->add_texture(std::static_pointer_cast<sg::texture>(tit->second));
  }
  else
  {
  // Assemble texture base directory
  - boost::filesystem::path texture_base_path;std::cout << std::string(mtl_name.begin(), mtl_name.length()) << '\n';
  + boost::filesystem::path texture_base_path;
  // Directory is probably stored in color map (use mtl_name to look this up!)
  auto cit = color_maps.find(std::string(mtl_name.begin(), mtl_name.length()));
  @@ -434,16 +447,6 @@ static void load_obj(
  }
  }
  }
  - }
  - else if ( qi::phrase_parse(it, text.cend(), grammar.r_usemtl, qi::blank, mtl_name) )
  - {
  - std::string usemtl = mtl_name.to_string();
  - auto it = materials.find(usemtl);
  - if (it != materials.end())
  - {
  - surf->material() = it->second;
  - }
  - }
  else if ( qi::phrase_parse(it, text.cend(), grammar.r_vertices, qi::blank, vertices) )
  {
  }
  