OSL 1.11.11.0

Release 1.11.11 -- 1 Feb 2021 (compared to 1.11.10)

• Build: Make the CMake build system more friendly to being a subproject.
  #1304
• Build: Improve dependency on Imath/OpenEXR include files.
• CI: Fixes to Mac CI. #1315
• Docs: Update CLAs, Charter, GOVERNANCE, particularly after acceptance of
  new CLAs and moving the repo to the ASWF GitHub account. #1308 #1240 #1314
• Internals: Switch from deprecated call to OIIO::parallel_image to the new
  version. #1317