Repeatables without labels

Closes #43
That is not tangential at all, since I "fixed" the behavior here. I went back and forth over this myself and eventually just gave up and deferred to what was in phpdoc:

```php
/**
 * @var int
 * How many of these fields to display initially, if $limit != 1
 */
public $starting_count = 1;

/**
 * @var int
 * How many extra elements to display if there is already form data and $limit != 1
 */
public $extra_elements = 1;
```

In retrospect, I think I agree with you, but this would probably be better termed `$minimum_count` and also come with a JS component to hide the "x"s when the minimum is hit (or change the behavior of the "x"s to clear the box). I could see it being confusing if there is a `'starting_count' => 3`, you remove all but one field and save, and three fields show up again.

I hate to say it because this is complicated enough as it is, but I wonder if we should add that as a separate option altogether. If we did so, I would be in favor of deprecating `$starting_count` (tbh, I'm not really sure how we could deprecate it). Or maybe that's not worth it, and we just change the behavior (and phpdoc) for `$starting_count`. I don't know.

@bcampeau, @netaustin your thoughts?