Secrets and lies (well, hostnames, anyway)

Been a while, hasn't it... anyway, we've got a few bugfixes, and some hawt container restart action.
But the reason you'll want to update is that you no longer have to store your secrets in the pod config file, but can inject them into the container's runtime config via a new `environment_files` container config hash.
Very secure, much wow, as the cool kids say.

Bugs squashed, happiness achieved

This release fixes a couple of small glitches in container freshness checking and
corner cases in image specifications.

Workaround IPv6 address limitation on the 'bridge' network

Container pruning and credential helper support

The final corner-case of "what happens when a running container is no longer in the
pod definition?" is implemented.  Also added support for fetching credentials from `config.json`
and credential helpers defined therein.

Add support for start-time health checking

Sometimes you just want to know that your containers are healthy before moving
on.  Now you can.

Tweaks and tidies

Now with root labels!

Make exposed ports actually work

Hurrah hurroo hurray!

Tweak Docker timeouts, command-line output

Fix /etc/resolv.conf mounting