Fully omit completely hidden nodes.

For instance:
```json
{
  "this is public": "public",
  "nested": {
    "this is private": "private",
    "this is super private": "super private"
  }
}
```

Should output:
```json
{
  "this is public": "public"
}
```

Rather than:
```json
{
  "this is public": "public",
  "nested": {}
}
```

This marks a version bump to 0.3.0.