[tz] Irish Standard Time vs Irish Summer Time

[Paul Eggert]

Michael Douglass wrote:
> we should be storing version information along with the dates and ids.
Starting with 2016g, releases have come with a file called 'version' that 
contains a version number. Starting with 2018a releases, this version number is 
also in the file 'tzdata.zi'. This version number can be used by downstream data 
parsers as needed; tzcode does not use it.

The development repository contains more-detailed information for all changes 
made to the published code or data since 1984.