Port of the 0.4.x site-url absolute-links patch to the 0.5 crates/ layout,
toward upstreaming as PR #1802. When output.html.site-url is set, internal
links and assets are emitted as absolute URLs anchored at site-url, so the
book works under a sub-path (e.g. /cdcidao/) regardless of page depth.
- html/tree.rs: fix_link/fix_html_link rewrite ./ content, image and raw-HTML
links to {site_url}...; schemes and fragments untouched
- html_handlebars/hbs_renderer.rs: path_to_root = site_url for normal and index
pages; base_url = site_url only for the toc.html iframe (removed before the
per-chapter clone so it cannot leak)
- html_handlebars/helpers/resources.rs: {{resource}} honors an explicit
path_to_root from data (absolute assets) with stock fallback
- html/print.rs: print page honors site-url; internal cross-refs still fold to
#anchors, non-chapter links keep absolute form
- cmd/serve.rs: --preserve-site-url flag; serve still forces site-url to / for
local preview but logs the override
- tests/testsuite/rendering*: site_url fixture + tests (content, assets, print,
no <base> leak, no-regression without site-url)
- guide: document the serve flag and the renderer behavior
0784554c88