message: Thin-lens camera for phantom example
diff: #include <visionaray/cpu_buffer_rt.h>
  #include <visionaray/kernels.h>
  #include <visionaray/material.h>
  -#include <visionaray/pinhole_camera.h>
  #include <visionaray/scheduler.h>
  +#include <visionaray/thin_lens_camera.h>
  #include <common/manip/arcball_manipulator.h>
  #include <common/manip/pan_manipulator.h>
  @@ -625,7 +625,7 @@ struct renderer : viewer_type
  }
  }
  - pinhole_camera cam;
  + thin_lens_camera cam;
  cpu_buffer_rt<PF_RGBA32F, PF_UNSPECIFIED> host_rt;
  tiled_sched<basic_ray<float>> host_sched;
  @@ -866,6 +866,8 @@ int main(int argc, char** argv)
  float aspect = rend.width() / static_cast<float>(rend.height());
  rend.cam.perspective(45.0f * constants::degrees_to_radians<float>(), aspect, 0.001f, 1000.0f);
  + rend.cam.set_lens_radius(0.002f);
  + rend.cam.set_focal_distance(2.0f);
  // Load camera from file or set view-all
  std::ifstream file(rend.initial_camera);
  