Rename backsplice -> ksonnet

Rename early and often.

Implement "update" subcommand

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

Rename package path bitnami/kubecfg -> backsplice/kubecfg

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.

Repo was (at least initially) published under bitnami/ - make imports
consistent with that path.

Basic skeleton.  Can evaluate jsonnet and show the output as yaml or
json .. and that's about it.