[tz] Add ISO Phonetic and Letter Time Zone Links to etcetera

[Matt Johnson-Pint]

> If we were to make changes in this area, I think I might prefer going 
> the other way and removing Etc entirely, as everything in Etc is either 
> confusing or redundant.

Please don't remove the fixed-hour time zones like Etc/GMT+2.  We need them for timekeeping on ships at sea.

They're also referenced in the Unicode CLDR Windows Zone mapping file.
https://github.com/unicode-org/cldr/blob/master/common/supplemental/windowsZones.xml

Also Etc/UTC is much needed for the cloud, and servers in general.

Thanks,
Matt