maintanence release

all

• C++ 17
• internal contrib/SampleICC cleanup, dropping auto_ptr

imgcat

• support heif/heic files via corresponding exiv2
• multi thread support via C++ async using host's max threads
• strip metadata from generated thumbnails
• generated thumbnails with correct orientation on non-preview (ie extracted from raw) files

imgprextr

• support common sizes for resize via -O
• do not overwrite existing files by default, with control via -f
• fix extensions on extracted files (no double extn: ie foo.nef.jpg)
• fix colour profile conversion bug on extracted images