Support has-error and is-error classes on checkboxes

[resurtm]

Hello!

Shouldn't checkboxes also support has-error and is-error classes? For example:

<div class="form-group has-error">
	<label class="form-checkbox">
		  <input type="checkbox"/>
		  <i class="form-icon"></i>
		  I confirm agreement with <a href="#">Terms of Services</a>
	</label>
</div>

The result checkbox should somehow have error state.

Cheers!

[picturepan2]

@resurtm Version 0.2.19 is released. Error and success states have been added to checkbox, radio and switch. https://picturepan2.github.io/spectre/elements.html#forms