support for an array request body

I've added support for the following example:

```console
$ curl http://example.com/config-vars \
  -X PATCH \
  -d '[
         {"name": "FOO", "value": "1"},
         {"name": "BAR", "value": "2"},
       ]'
```
Since data is hardly used I think we can simplify by just doing `data = schema.schema_example(link['schema'])` here, but to do that well we should nuke the earlier definition of data and change the `empty?` checks to `nil?`, I think anyway. What do you think?