cluster/kube: split up cluster.jsonnet

It was getting large and unwieldy (to the point where kubecfg was slow).
In this change, we:

 - move the Cluster function to cluster.libsonnet
 - move the Cluster instantiation into k0.libsonnet
 - shuffle some fields around to make sure things are well split between
   k0-specific and general cluster configs.
 - add 'view' files that build on 'cluster.libsonnet' to allow rendering
   either the entire k0 state, or some subsets (for speed)
 - update the documentation, drive-by some small fixes and reindantation

Change-Id: I4b8d920b600df79100295267efe21b8c82699d5b
diff --git a/cluster/kube/k0-registry.jsonnet b/cluster/kube/k0-registry.jsonnet
new file mode 100644
index 0000000..a2a6061
--- /dev/null
+++ b/cluster/kube/k0-registry.jsonnet
@@ -0,0 +1,3 @@
+// Only the registry running in k0.
+
+(import "k0.libsonnet").k0.registry