Chores/matcher cleanup

[shamus]

Prior to this PR, the matchers used a simplified interface to make assertions, but this proved difficult to extend.

This PR brings the k8s matchers closer to the underlying structure of the data resulting from parsing the resulting YAML. This should ease both the extension of the matchers and their expressiveness.

[cf-gitbot]

We have created an issue in Pivotal Tracker to manage this:

https://www.pivotaltracker.com/story/show/170669099

The labels on this github issue will be updated when the story is started.

[andrewedstrom]

I like this. I like that the structure of the matcher calls mimics the structure of the generated yaml.

I think this is quite readable:

		Expect(ctx).To(
			ProduceYAML(
				RepresentingDeployment().WithPodMatching(func(pod *PodMatcher) {
					pod.WithContainerMatching(func(container *ContainerMatcher) {
						container.WithName("uaa")
					})
				}),
			),
		)