doc: make the api doc print-friendly

Fixes: https://github.com/nodejs/node/issues/6743

PR-URL: https://github.com/nodejs/node/pull/6748


Reviewed-By: Robert Jefe Lindstaedt <robert.lindstaedt@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Stephen Belanger <admin@stephenbelanger.com>
Reviewed-By: Myles Borins <myles.borins@gmail.com>