Implement directive for form validation

[iErik]

Currently we have two ways to define form validation rules using the FormValidator mixin:

• By providing a validation option object in the root of the component, containing the validation rules for the component forms, whether scoped or not.

• By calling the this.$validator.init(<options object>) method from the component. The $validator.init method accepts a option object that follows the same standard as the validation option object in the root of the component.

Bu perhaps we could also add a way for the user to define it's validation rules in the template, using a directive:

<input
  type="text"
  name="fullName"
  v-validator="required"
  v-model="fullName"
/>

Although the library would no longer be strictly model-based nor completely decoupled from templates, using a directive may be a better option for smaller forms.