Function build_program_man_page 

pub fn build_program_man_page(
    cmd: &Command,
    prog_name: &str,
    version: &str,
    description: Option<&str>,
    docs_url: Option<&str>,
) -> String

Build a complete roff man page for the entire CLI program.

Covers all registered commands including downstream business commands. The cmd should be the fully-built root clap::Command.