Old style. Make it compliant with our code review comments document.

Also, make WriteString's return parameter named 'n', not 'ret', for
consistency.

Noticed during another documentation review.

Change-Id: Ie88910c5841f8353bc5c0152e2168b497578e15e
Reviewed-on: https://go-review.googlesource.com/12324Reviewed-by: Rob Pike <r@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>