Enable a different announcement for premium releases

Enable a different announcement for premium releases

The basic data of what is considered premium and what is considered
public releases, a new bash function is added, std_release_type(), found in
release-tools/release-aux/release-data-fn.sh.

Along with this, the non-descript variable 'tag' is renamed to 'release_tag',
and a spelling error is corrected.

Fixes #157

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/tools/pull/160)