Allow merging of nested JSON structures in multiple config files

[brodo]

It there are two config files f1.json and f2.json which look like this:

f1.json:

{
  "nested": {
    "a": true,
    "b": "test"
  }
}

f2.json:

{
  "nested": {
    "b": "test2"
    "c": 123
  }
}

And json_env is called like this: json_env -c f1.json -c f2.json ....

The resulting merged file should look like this:

{
  "nested": {
    "a": true
    "b": "test2"
    "c": 123
  }
}