1. Add commands to navigate between man page links.
2. Add command to jump to a man page by following a man page link.
3. Add key map for <ret> to jump command.
4. Add key maps for a suggested user mode.
1. If there is no man page found (error 16), then echo stderr text.
2. For other kinds of errors, fail with stderr text so that command can propagate through a try/catch.
