Add standalone markdown preprocessor to generate manpages without requiring
mdbook's Rust toolchain. This removes a significant build dependency for
manpage generation while keeping the HTML manual (mdbook) working unchanged.
Changes:
- Add expand-includes.py: Python 3 script that recursively expands
{{#include}} directives, resolves @docroot@ to nix.dev URLs, and handles
@generated@/ paths for build-generated files
- Update render-manpage.sh: Replace mdbook-based implementation with
standalone version that uses expand-includes.py + lowdown
- Update meson.build: All 134 manpage targets now use standalone renderer
with proper dependencies (expand-includes.py, experimental-features-shortlist)
- Fix nix-hash.md: Remove extra parenthesis in markdown link syntax
Benefits:
- No mdbook/Rust toolchain required for manpage builds
- Manpages contain nix.dev/latest URLs instead of broken relative paths
- Fixes bug where mdbook didn't expand experimental-features-shortlist.md
- 98.5% identical output to mdbook (2 files differ, both acceptable)
All 134 manpages (131 section 1, 2 section 5, 1 section 8) build successfully.
