OSPRay v1.5.0

• TetrahedralVolume now generalized to take both tet and hex data, now called
  UnstructuredVolume
• New function for creating materials (ospNewMaterial2) which takes the
  renderer type string, not a renderer instance (the old version is now
  deprecated)
• New tonemapper PixelOp for tone mapping final frames
• Streamlines now support per-vertex radii and smooth interpolation
• ospray_sg headers are now installed alongside the SDK
• Core OSPRay ispc device now implemented as a module
  • Devices which implement the public API are no longer required to link
    the dependencies to core OSPRay (e.g. Embree v2.x)
  • By default, ospInit will load the ispc module if a device was not
    created via --osp:mpi or --osp:device:[name]
• MPI devices can now accept an existing world communicator instead of always
  creating their own
• Added ability to control ISPC specific optimization flags via CMake options
  • See the various ISPC_FLAGS_* variables to control which flags get used
• Enhancements to sample applications
  • ospray_sg (and thus ospExampleViewer/ospBenchmark) can now be
    extended with new scene data importers via modules or the SDK
  • Updated ospTutorial examples to properly call ospRelease()
  • New options in the ospExampleViewer GUI to showcase new features
    • SRGB frame buffers, tone mapping, etc.
• General bug fixes
  • Fixes to geometries with multiple emissive materials
  • Improvements to precision of ray-sphere intersections