• backend: async completion callbacks now take a backend::AsyncCallStatus argument reporting
  whether the operation ran (COMPLETED) or was canceled (CANCELED). Callers chaining work from
  a completion callback must check it [⚠️ API Change]
• backend: canceling an async call now always invokes its completion callback, with
  AsyncCallStatus::CANCELED. Previously the callback was silently dropped
• engine: fix picking on PowerVR OpenGL ES drivers that mishandle dynamic uniform-buffer indexing
  in fragment shaders [⚠️ Recompile Materials]
• engine: support multiple directional lights, opt-in via
  Engine::Config::enableMultipleDirectionalLights; the dominant one still provides shadows and
  the sun disc, up to 4 additional directional lights are evaluated without shadows [⚠️ New
  Material Version]
• materials: a second specular lobe can be defined by setting the secondRoughness and
  secondRoughnessWeight properties. This can be used to create hazy materials. These properties
  require material to declare apiLevel : 2 (or greater).
• filamat: completely remove the DYN variant bit.[⚠️ Recompile Materials]