Python bindings to libheif for working with HEIF images and plugin for Pillow.

Features:
- Decoding of 8, 10, 12 bit HEIC and AVIF files.
- Encoding of 8, 10, 12 bit HEIC and AVIF files.
- EXIF, XMP, IPTC read & write support.
- Support of multiple images in one file and a PrimaryImage attribute.
- Adding & removing thumbnails.
- Reading of Depth Images.
- Adding HEIF support to Pillow in one line of code as a plugin.