Added

• cli: Added a percentage display in watch mode
• Added a flake.nix for Nix users

Changed

• structs3: Added an additional test
• macros: Added a link to MacroKata in the README

Fixed

• strings3: Added a link to std in the hint
• threads1: Corrected a hint link
• iterators1: Clarified hint steps
• errors5: Fix a typo in the hint
• options1: Clarified on the usage of the 24-hour system
• threads2, threads3: Explicitly use Arc::clone
• structs3: Clarifed the hint
• quiz2, as_ref_mut, options1, traits1, traits2: Clarified hints
• traits1, traits2, cli: Tidied up unmatching backticks
• enums2: Removed unneccessary indirection of self
• enums3: Added an extra tuple comment

Housekeeping

• Added a VSCode extension recommendation
• Applied some Clippy and rustfmt formatting
• Added a note on Windows PowerShell and other shell compatibility