This removes all objects listed in config files (and dependents) -
effectively reversing an `update --create`.

Intended for short-lived "try this out; now clean up" workflows.

Fixes #14

There is some variation in jsonnet "result" conventions.  This change
assumes the top level is a JSON object, and then walks down looking
for objects with `apiVersion` & `kind` fields.

While walking down, the current code will expand JSON arrays, and
object values.

In particular, this should correctly accept:
- single-value JSON files
- arrays (jsonnet --yaml-stream)
- "filename->object" objects (jsonnet --multi)

(Note that any v1.Lists encountered are still expanded in a
second-pass, as before)

The goal is to make a best-effort attempt at reducing the number of
"crash-restart" loops required to bring up a group of interdependent
resources.

The current implementation is very simple and just sorts into 3 tiers:
- Namespace, ThirdPartyResource, StorageClass
- everything else
- Pods or similar (Pod/Job/Deployment/DaemonSet/StatefulSet)

- Support the standard client-go/kubectl flags
- Switch object types to use client-go rather than apimachinery
- Implement update subcommand

File format is recognised via simple file extension check.

Any "List" objects found will be expanded into their constituent
items, so single-element formats like json and jsonnet can use a
v1.List to capture multiple resource objects.