• Added linear cone curve geometry support. In this mode a real geometric surface for curves
  with linear basis is rendered using capped cones. They are discontinuous at edge boundaries.
• Enabled fast two level builder for instances when low quality build is requested.
• Bugfix for BVH build when geometries got disabled.
• Added EMBREE_BACKFACE_CULLING_CURVES cmake option. This allows for a cheaper round
  linear curve intersection when correct internal tracking and back hits are not required.
  The new cmake option defaults to OFF.
• User geometries with invalid bounds with lower>upper in some dimension will be ignored.
• Increased robustness for grid interpolation code and fixed returned out of range u/v
  coordinates for grid primitive.
• Fixed handling of motion blur time range for sphere, discs, and oriented disc geometries.
• Fixed missing model data in releases.
• Ensure compatibility to newer versions of oneTBB.
• Motion blur BVH nodes no longer store NaN values.