v0.2.3

This is the last version with macOS and Windows support. Future versions will be Linux-only, using GTK4 and WebKitGTK 6.0.

Changes

• Temp files are now written to system temp directory instead of next to the markdown file (#2, #11) — thanks @cuducos
• Temp directory is cleaned up on window close
• Updated nixpkgs flake to fix WebKitGTK EGL crash on Wayland
• Added flake.nix for Nix-based development and builds