fn install_mdbook_epub(cache: &Path, local_bin: &Path, rev: &str) -> Result<()>Expand description
Builds and installs mdbook-epub from source if the cached revision is stale.
The binary is placed at ~/.cache/mdbook-epub/bin/mdbook-epub and
symlinked into ~/.local/bin/. A .rev file records the installed SHA so
subsequent runs can detect staleness without rebuilding.