Rename hosts to hostname, which also writes /etc/hostname (hq ADR 0223)

Two files say one fact, the machine's name, and nothing owned /etc/hostname.
The name written is the operator's hostname setting, with no default: three
of four machines call themselves something other than their mesh name, and
renaming one is the operator's call. It takes effect at the next boot.

modules/hostname/module.json

@@ -0,0 +1,48 @@
+{
+  "module": "hostname",
+  "version": "1",
+  "claims": [
+    {
+      "name": "node-hostname",
+      "scope": "node",
+      "serves": [
+        "entries",
+        "add",
+        "remove"
+      ]
+    }
+  ],
+  "resources": [
+    {
+      "id": "own",
+      "type": "file",
+      "path": "/etc/hosts",
+      "mode": "0644",
+      "into": "block",
+      "at": "start",
+      "content": "# The machine's own names (module hostname, novox/hq ADR 0199, ADR 0223). Every line outside this\n# block is the operator's: kept across every push, changed through the node-hostname verbs add and\n# remove, and given back when this module goes. The mesh's names are not here: the mesh's resolver\n# answers them.\n127.0.0.1\tlocalhost\n::1\tlocalhost\n127.0.1.1\t${machine:name}\n"
+    },
+    {
+      "id": "name",
+      "type": "file",
+      "path": "/etc/hostname",
+      "mode": "0644",
+      "content": "${setting:hostname}\n"
+    }
+  ],
+  "build": {
+    "artifacts": [
+      {
+        "name": "tools",
+        "kind": "bundle",
+        "language": "go",
+        "system": "arch",
+        "from": "cmd/hostname-tools",
+        "binary": "hostname-tools",
+        "loads": [
+          "hostname-tools"
+        ]
+      }
+    ]
+  }
+}