message: generate-obj: Use <filesystem> for the output filenames
diff: #include "opencv2/highgui/highgui.hpp"
  #include <iostream>
  +#include <filesystem>
  using namespace eos;
  +namespace fs = std::experimental::filesystem;
  using std::vector;
  using std::cout;
  using std::endl;
  @@ -88,11 +90,12 @@ int main(int argc, char *argv[])
  core::Mesh sample_mesh = morphable_model.draw_sample(shape_coefficients, colour_coefficients); // if one of the two vectors is empty, it uses get_mean()
  - core::write_obj(sample_mesh, output_file.string());
  + core::write_obj(sample_mesh, output_file);
  core::Image4u rendering;
  std::tie(rendering, std::ignore) = render::render(sample_mesh, glm::mat4x4(1.0f), glm::ortho(-130.0f, 130.0f, -130.0f, 130.0f), 512, 512, std::nullopt, true, false, false);
  - output_file.replace_extension(".png");
  - cv::imwrite(output_file.string(), core::to_mat(rendering));
  + fs::path filename_rendering(output_file);
  + filename_rendering.replace_extension(".png");
  + cv::imwrite(filename_rendering.string(), core::to_mat(rendering));
  cout << "Wrote the generated obj and a rendering to files with basename " << output_file << "." << endl;
  