Better names for Guix versions from git?

[Taylan Kammer]

Currently, after running 'guix pull', the Guix version will be reported
by 'guix --version' as something like:

    522d1b87bc88dd459ade51b1ee0545937da8d3b5

I think it would be really nice if instead it were something like:

    2018-12-25-522d1b

where the date is the commit's date (year, month, day) in UTC+0.

That's shorter, more descriptive, and just as unique.  (The chances of
there being two commits in the same day with the same first 6 positions
in the hash should be negligient.)

The package name is currently something like:

    guix-522d1b87b

That could become:

    guix-2018-12-25-522d1b

which is a bit longer but more descriptive.

I looked into guix/self.scm a bit but couldn't easily tell how difficult
it would be to implement these changes.

Thoughts?  Worth it?


Taylan