internal/export/idna: improved naming, docs, and examples.

I hope this makes it a bit clearer.

Documentation with the ToASCII and ToUnicode functions
has been removed to avoid suggesting that this behavior is
specific to the Punycode Profile.

Renamed UseSTD3Rules to the more descriptive StrictDomainName.
Other possible names are StrictASCII or just DomainName.

Change-Id: Iec8e8d4dd6c8f4ebda71c2894a199c9203f263db
Reviewed-on: https://go-review.googlesource.com/36871
Run-TryBot: Marcel van Lohuizen <mpvl@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Nigel Tao <nigeltao@golang.org>
3 files changed