ACF Group

would be good if we could get a `Group` field in the library

as far as I know it just prefixes `groupname_` so if eg my Group is `hero` and my first field in the repeater is `image` then the field becomes `hero_image`

I had a go at adapting the Repeater field and it seemed to work using eg
```
protected function fetchPostsMeta($fieldName, $post) {
....
$builder->where(function ($query) use ($fieldName) {
$query->orWhere('meta_key', 'REGEXP', "^{$fieldName}_[a-z0-9]*$");
});
```

```
protected function fetchFields ($fieldName, Builder $builder) {
...
$name = str_replace($this->name."_", '', $name);
$fields[$name] = $field->get();
```

I hope this of some use. It's mostly trial and error, I'm not quite sure how the whole thing fits together.