adding the libarchive_ruby gem to debianpackages

[Hans Mackowiak <hanmac@gmx.de>]

hy there i build a gem for the compressing libachive
my git can you see there: https://github.com/Hanmac/libarchive-ruby
i hope you add this to debian.
it needs a ruby version >=1.8.7 because of Enumerator, but >=1.9.2 is
prevered

--Hanmac