Ensure that AUTHORS and ChangeLog are packaged

Include AUTHORS and ChangeLog from pbr to be included
in the sdist tarball. Add a minimal HACKING.rst for
consistency with other projects.

Fixes LP Bug #1186518

Change-Id: I0f188c1c1b449b74b43296222d33a89f98645950
Merge "Ensure that AUTHORS and ChangeLog are packaged"