umoci 0.4.6

umoci has been adopted by the Open Container Initative as a reference
implementation of the OCI Image Specification. This will have little impact
on the roadmap or scope of umoci, but it does further solidify umoci as a
useful piece of "boring container infrastructure" that can be used to build
larger systems.

NOTICE: As part of the adoption procedure, the import path and module
name of umoci has changed from github.com/openSUSE/umoci to
github.com/opencontainers/umoci. This means that users of our (still
unstable) Go API will have to change their import paths in order to update
to newer versions of umoci.

The old GitHub project will contain a snapshot of v0.4.5 with a few
minor changes to the readme that explain the situation. Go projects which
import import the archived project will receive build warnings that
explain the need to update their import paths.

• umoci now builds on MacOS, and we currently run the unit tests on MacOS to
  hopefully catch core regressions (in the future we will get the
  integration tests running to catch more possible regressions).
  #318

• Suppress repeated xattr warnings on destination filesystems that do not
  support xattrs. #311
• Work around a long-standing issue in our command-line parsing library (see
  urfave/cli#1152) by disabling argument re-ordering for umoci config,
  which often takes --prefixed flag arguments. #328

Thanks to all of the people who made this release possible:

• Aleksa Sarai asarai@suse.de
• David Trudgian dave@trudgian.net
• Ramkumar Chinchani rchincha@cisco.com
• Tycho Andersen tycho@tycho.ws

LGTMs: @cyphar @tych0
Signed-off-by: Aleksa Sarai asarai@suse.de