[tz] Version identification (was Re: Downstream use of 2021c)

[Paul Eggert]

On 10/7/21 13:41, Arthur David Olson via tz wrote:
> One odd possibility on standardizing access to version information: a 
> zic'd line such as...
>      Zone Version 0 - 2021c
> ...would allow use of the command...
>     TZ=Version date
> ...to discover the version.-)

Clever! I hadn't thought of that. This could supplant the "# version" 
line in tzdata.zi, and I suppose a similar trick could be used for the 
"# redo", "# ddeps", and "# dataform" lines - though this would limit us 
to ASCII alphanumerics and '-' and '+' in version numbers, which could 
be a bit restrictive.