"xo" need option to make JSON object wrapper

[philshafer]

$ xo --wrap "a/b/c" --json --pretty "{:name}{:value}\n" one a
"a": {
  "b": {
    "c": {
      "name": "one",
      "value": "a"
    }
  }
}

which isn't a complete json object. A "--object-wrapper" option should put the entire output inside a "{}" wrapper. This should be true for "--open" and "--close" as well.

[philshafer]

This is in the "develop" branch as "--top-wrap".

Thanks,
Phil