Support for nested JSON objects

The Alteryx promote-python library supports nested JSON objects:

```
{
"name": {
"first_name": "colin",
"last_name": "kaepernick"
}
}
```

This doesn't work in the R client though. The jsonlite package supports nested JSON, but for some reason it is being flattened for the promote request:

```
{
"name.first_name": "colin",
"name.last_name": "kaepernick"
}
```

Is there any reason for flattening the JSON here (and not in python) ?