In addition to the "normal" ELPA git directories, I created
a directory tar-archives.
In this directory one should put tar-balls of the different versions
of the ELPA library.

Since the tar-balls "loose" the git history and are only a snapshot
of the respective version at the time of creation, one should name
the tar balls accordingly.

I opted now for the naming of

ELPA_VERSION_day_month_year_of_creation.tar.gz, e.g with the commit
from today (17/06/2013) I created from the ELPA_VERSION "ELPA_2011.12"
a tar ball named "ELPA_2011.12_17062013.tar.gz".