OpenImageIO 2.2.17.0

Release 2.2.17 (1 Aug 2021) -- compared to 2.2.16

• Output to DPX files now supports IOProxy. (Input already did.) #3013
• typedesc.h: TypeDesc can now describe 2D and 3D bounding boxes, as arrays
  of 2 VEC2 aggregates (for 2D) or VEC3 aggregates (for 3D) with "BOX"
  semantic. The shorthand for these are TypeBox2, TypeBox3 (for float),
  and TypeBox2i and TypeBox3i for integer or pixel coordinte
  boxes. #3008
• Build: Fixes for building against fmt 8.0.0. #3007
• Build: Finding boost is more flexible when desiring static libraries. #3031