Async Validator

[stuyam]

Ability to define async validators that are called with callbacks and and get called after regular validation happens.

References: #98 from @ej2015.
Got this branch working.

Usage

1. Define rule

this.validator = new SimpleReactValidator({
  validators: {
    unique: {
      message: 'Not a unique email.',
      asyncRule: function(val, params, validator, completion) {
        // call validator.pass(completion) to pass onto next async validator or pass validation
        // call validator.fail(completion) if something goes wrong
        setTimeout(() => validator.fail(completion), 1000);
      }
    }
  }
});

2. Add to message

{this.validator.message('email', this.state.email, 'email|unique')}

3. New pass fail completion blocks

submitForm() {
  this.setState({processing: true});
  this.validator.asyncValid({
    pass: () => {
      alert('You submitted the form and stuff!');
      this.setState({processing: false});
    },
    fail: () => {
      this.validator.showMessages();
      this.setState({processing: false});
    }
  });
}

[stuyam]

@ej2015 I am not as familiar with promises so not sure if I would be able to use one in this case to clean it up?