• Added EMBREE_ISA_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.