message: Don't use pnm_image directly
diff: #include <common/inifile.h>
  #include <common/make_materials.h>
  #include <common/model.h>
  -#include <common/pnm_image.h>
  +#include <common/image.h>
  #include <common/sg.h>
  #include <common/timer.h>
  #include <common/viewer_glut.h>
  @@ -2176,14 +2176,14 @@ void renderer::on_key_press(key_event const& event)
  }
  }
  - pnm_image img(
  + image img(
  rt.width(),
  rt.height(),
  PF_RGB8,
  reinterpret_cast<uint8_t const*>(rgb.data())
  );
  - pnm_image::save_option opt1({"binary", true});
  + image::save_option opt1({"binary", true});
  if (img.save(screenshot_filename, {opt1}))
  {
  std::cout << "Screenshot saved to file: " << screenshot_filename << '\n';
  