Release 2.2.8.0

Release 2.2.8 (1 Nov 2020) -- compared to 2.2.7

• Fix that ImageBuf images backed by ImageCache, could hold an outdated copy
  of the image if it was in the imagecache once, then changed on disk. #2696
• Fix stack overflow crash in IBA::colorconvert of unusually wide images.
  #2716
• Fix boost linkage problem on Windows. #2727
• Fix broken reads of 16 bit iff files. #2736
• Fix make_texture incorrectly setting tile sizes. #2737
• Fix incorrect ARM NEON code in simd.h. #2739
• Improve oiiotool --chappend and --siappend, allowing an optional modifier
  ":n=" to specify the number of images from the stack to be combined by
  having their channels or subimages appended. #2709
• WebP: add support for requesting compression "lossless". #2726
• Improve build system for finding Python, now if a specific version is not
  requested, default to whichever is found rather than always defaulting to
  Python 2.7. #2705 #2764
• Fix deprecation warnings when building with very new PugiXML versions.
  #2733
• Fix ImageCache bug: add_tile/get_tile not properly honoring when
  chend < chbegin it should get all channels. #2742
• Fix build break when strutil.h was included in Cuda 10.1 code. #2743
• Docs: Make readthedocs generate downloadable htm as well as pdf. #2746
• Improve oiiotool's guessing about the desired output format based on
  inputs (in the absence of -d to specify the format). #2717
• JPEG output: add support for writing progressive JPEGS (set the
  attribute "jpeg:progressive" to 1). #2749
• WebP input improvements including: RGB images are kept as RGB instead of
  always adding alpha; more efficient by skipping alpha premultiplication
  when it's unnecessary; now can read animated WebP images as multi-subimage
  files. #2730
• Docs: ImageInput chapter now has an example of reading image data into
  separate per-channel buffers. #2756
• Fixes to build against recent changes in OpenColorIO v2 master. #2765