[Libguestfs] [PATCH libnbd 0/4] Miscellaneous Rust cleanups

Add an overview libnbd-rust(3) man page pointing to the real documentation. This is like OCaml & Golang. When reviewing the real rustdocs I noticed they basically converted the man pages into plain text, resulting in lots of problems such as internal links not working, no `code` annotations, etc. So I wrote a simple POD to rustdoc translator. It is by no means perfect, but it fixes many of the issues. Also build the examples, to make sure we don't get any regressions. Rich.