v1.8.0 - faster AVIF with rav1e, gdk-pixbuf with AVIF, nclx color profile handling

• Integration of rav1e encoder for faster AVIF encoding
• gdk-pixbuf loader now supports AVIF decoding
• color conversion adapts to nclx color profile
• new parameters for heif-enc to set nclx parameters
• support for saving in RGB colorspace (matrix_coefficients=0) for true lossless encoding
• chroma 4:2:2 and 4:4:4 encoding for HEIF
• chroma 4:2:2 and 4:4:4 with AVIF, also with HDR
• monochrome AVIF encoding with AOM plugin
• changed AVIF bitrate control depending on quality parameter
• support for AVIFs with depth images
• AVIF MIME type detection
• update Go API for HDR images
• write libheif and plugin version info to HEIF/AVIF headers
• fix problems with odd image resolutions and very small image sizes
• fix writing too much data into alpha channel images
• lots of bug fixes and handling of corner cases