ImageIO Format PNG: cleanup
ImageIO Format PNG: 8bit: avoid additional buffer copying.
Let libpng remove alpha.
ImageIO Format PNG: 16bit: avoid additional buffer copying.
Let libpng remove alpha and swap bytes.
ImageIO Format PNG: refactor common code
usermanual: reflect recent changes to the exposure module
usermanual: fix for #10148
usermanual: some more details on color zones
usermanual: more on the concepts of pixelpipe, module order and history stack
Merge pull request #693 from LebedevRI/imageio-format-png-update

Imageio format png update