Embree

- Restored binary compatibility between Embree 3.6 and 3.5 when single-level instancing is used.
- Fixed bug in subgrid intersector
- Removed point query alignment in Intel® ISPC header

- Added Catmull-Rom curve types.
- Added support for multi-level instancing.
- Added support for point queries.
- Fixed a bug preventing normal oriented curves being used unless timesteps were
specified.
- Fixed bug in external BVH builder when configured for dynamic build.
- Added support for new config flag "user_threads=N" to device initialization
which sets the number of threads used by Intel® TBB but created by the user.
- Fixed automatic vertex buffer padding when using rtcSetNewGeometry API function.

- Added EMBREE_API_NAMESPACE cmake option that allows to put all Embree API functions
inside a user defined namespace.
- Added EMBREE_LIBRARY_NAME cmake option that allows to rename the Embree library.
- When Embree is compiled as static library, EMBREE_STATIC_LIB has no longer to get
defined before including the Embree API headers.
- Added CPU frequency_level device configuration to allow an application to specify the
frequency level it wants to run on. This forces Embree to not use optimizations that
may reduce the CPU frequency below that level. By default Embree is configured to the
the AVX-heavy frequency level, thus if the application uses solely non-AVX code, configuring
the Embree device with "frequency_level=simd128" may give better performance.
- Fixed a bug in the spatial split builder which caused it to fail
for scenes with more than 2^24 geometries.

- Fixed ray/sphere intersector to work also for non-normalized rays.
- Fixed self intersection avoidance for ray oriented discs when
non-normalized rays were used.
- Increased maximal face valence for subdiv patch to 64 and reduced stack size
requirement for subdiv patch evaluation.

- Changed normal oriented curve definition to fix waving artefacts.
- Fixed bounding issue for normal oriented motion blurred curves.
- Fixed performance issue with motion blurred point geometry.
- Fixed generation of documentation with new pandoc versions.

- Added point primitives (spheres, ray-oriented discs, normal-oriented discs).
- Fixed crash triggered by scenes with only invalid primitives.
- Improved robustness of quad/grid-based intersectors.
- Upgraded to Intel® TBB 2019.2 for release builds.