feat: add areaId, ariaLabelledby options

[marcysutton]

This PR introduces two options: an areaId where you can provide an ID attribute for the textarea for binding with a native <label> element. While I was in there I also added an ariaLabelledby option to make it easier to use an existing element like a heading to name the textarea.

Markup case 1: areaId

<label for="thing1">Play with the code</label>
<textarea id="thing1"></textarea>

Markup case 2: ariaLabelledby

<h2 id="thing2">Play with the code</h2>
<textarea aria-labelledby="thing2"></textarea>

Developers can now choose either of those methods with the areaId and ariaLabelledby options, respectively.

Closes #78

[kazzkiq]

Published in: v1.2.0

Thanks!