Add validateIfErrored spec. Use case:

	<input
	 ng-model="user.name"
     ng-blur="user.validate('name')
	 ng-change="user.validateIfErrored('name')>

This will cause the input only to validate initially on blur, but, if the input contains errors, it will cause the input to validate on change. In this way, errors stay out of the user's face when false, and will immediately remove themselves when the user fixes them.
Add validateIfErrored method to ActiveResource::Base
Add Eventable mixin
Add validations to example application