doc: add `added:` information for os

Via git spelunking, mostly.
Some functions have been renamed. Used the version in which they were
renamed.

Ref: https://github.com/nodejs/node/issues/6578
PR-URL: https://github.com/nodejs/node/pull/6609


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Stephen Belanger <admin@stephenbelanger.com>