doc: reformat & improve node.1 manual page

Uses better troff formatting.
Removes v8 options from the man page.

Also edits `node -h` in node.cc slightly.

PR-URL: https://github.com/nodejs/node/pull/5497


Reviewed-By: James Snell <jasnell@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>