…instead of building a release tarball over and over again.
This has become an issue as meson insists on running tests before creating a
release tarball (which is a good policy).
related to #4086
The resulting packages are pushed to Debian repositories hosted on
bintray.com.
This is the first step to move away from our custom buildbot setup (see
https://i3wm.org/docs/buildbot.html for details on that) towards
infrastructure which is more standard (travis) and in the open.
