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.
* Adding HEIF support to Pillow in one line of code as a plugin.