[Bug 1434779] Add package for rebar3

https://bugzilla.redhat.com/show_bug.cgi?id=1434779

--- Comment #8 from Timothée Floure  ---
(In reply to Peter Lemenkov from comment #7)
> (In reply to John Eckersberg from comment #4)
> > I started down this path and basically ended up where you are now.  It would
> > be better to be able to bootstrap rebar3 using rebar 2.x, but I just gave up
> > and used a bootstrap rebar3 build from upstream releases.
>
> Yes, I think it's better (faster, and easier for us) to start from scratch
> rather than relying on rebar2 for boostrapping.

Thanks for the response! Then I will submit the related packages for reviews
during the next few days (currently backpacking on my way to flock). I will
gladly add anyone as co-maintainer once the packages reach the stable
repositories.