This release promotes package layering to `rpm-ostree install`, and
marks it as fully supported.  Garbage collection of the package cache
is implemented.

There are some other small changes such as no longer printing
the RPM changelogs from `db diff` anymore by default, which is long
overdue.

Git-EVTag-v0-SHA512: 6adb8de16b5d5c00a4034aaf38b0de537b2987898d96261297b5744307f2a2018621717ebf4b6073527a611d1effd9d534d2b04ed00320d876055871f0a33041