message: avoid using relative paths internally
diff: #include <utility>
  -#include <visionaray/math/forward.h>
  -#include <visionaray/math/matrix.h>
  -#include <visionaray/math/vector.h>
  -#include <visionaray/packet_traits.h>
  -#include <visionaray/matrix_camera.h>
  -#include <visionaray/pixel_format.h>
  -#include <visionaray/pixel_sampler_types.h>
  -#include <visionaray/render_target.h>
  -#include <visionaray/result_record.h>
  -
  +#include "../math/forward.h"
  +#include "../math/matrix.h"
  +#include "../math/vector.h"
  +#include "../packet_traits.h"
  +#include "../matrix_camera.h"
  +#include "../pixel_format.h"
  +#include "../pixel_sampler_types.h"
  +#include "../render_target.h"
  +#include "../result_record.h"
  #include "macros.h"
  #include "pixel_access.h"
  #include "tags.h"
  