Release 0.2 of guile-openai

This is the first proper release of guile-openai, a Guile Scheme library
providing a convenient high-level interface for interacting with the
OpenAI API.

Features:
 - High-level scheme interfaces for Chat, Image, Edit and Moderation APIs
 - Support for streaming responses, providing a familiar chat experience
 - Integration with Geiser for inline image display inside Emacs
 - Integration with ImageMagick for image optimization & conversion

Please note that this release introduces a GNU Autotools build system,
so old Guix package recipes using guile-build-system won't work.  An
updated package recipe is provided in the repository.

Thanks in particular to Aleix Conchillo Flaqué for the excellent
guile-json library which forms the backbone of this project, and Ricard
Wurmus for guile-picture-language and guile-studio which inspired this
library's focus on interactivity.