doc: improvements to console.markdown copy

Fix missing links. Fix styling of printf() - once #5073 lands,
link to man page will be auto-generated. Fix several typos.

PR-URL: https://github.com/nodejs/node/pull/5225


Reviewed-By: Roman Reiss <me@silverwind.io>
Reviewed-By: James M Snell <jasnell@gmail.com>