Hi

I have issues creating sns subscriptions through Cloudformation. If I attempt to include a `AWS::SNS::Subscription` resource in a Cloudformation template and run `create-stack` then I get a 500 Internal Server error. The full template:

```
AWSTemplateFormatVersion: '2010-09-09'
Description: 'Test'
Resources:
  MySnsTopic:
    Type: AWS::SNS::Topic
    Properties:
      TopicName: MySnsTopic
  MySnsTopicSubscription:
    Type: AWS::SNS::Subscription
    Properties:
      Protocol: sqs
      TopicArn: !Ref MySnsTopic
      Endpoint: !GetAtt
        - MySqsQueue
        - QueueArn
  MySqsQueue:
    Type: AWS::SQS::Queue
    Properties:
      QueueName: MySqsQueue
```

If I replace the references with hard-coded arns like this:

```
TopicArn: arn:aws:sns:eu-west-2:123456789012:MySnsTopic
Endpoint: arn:aws:sqs:elasticmq:000000000000:MySqsQueue
```

Then I get no errors but I get a warning:

`No moto Cloudformation support for AWS::SNS::Subscription`.

I can get around this issue by creating the subscription when creating the topic but the issue there is that I cannot add any attributes and in my case I need `RawMessageDelivery` set to true. So my questions are:

1. Is there no support to create `AWS::SNS::Subscription` resources through Cloudformation or am I doing something wrong?
2. If support is not there can I request it as a new feature?
3. Any suggestions on how I can work around this? I know I could do this through a script at startup but would like to not have any additional script steps other than deploying the Cloudformation stack.

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aws_stack.connect_to_service('sns').subscribe(
                TopicArn=topic_arn, Protocol=subscription['Protocol'], Endpoint=endpoint)
    elif resource_type == 'S3::Bucket':
        tags = resource_props.get('Tags')
        if tags:
            aws_stack.connect_to_service('s3').put_bucket_tagging(
                Bucket=params['Bucket'], Tagging={'TagSet': tags})
    return result
def deploy_template(template, stack_name):
    if isinstance(template, string_types):
        template = parse_template(template)
    resource_map = template.get('Resources')
    if not resource_map:
        LOG.warning('CloudFormation template contains no Resources section')
        return
    next = resource_map
    iters = 10
    for i in range(0, iters):
        
        for resource_id, resource in next.items():
            stack_resource = describe_stack_resource(stack_name, resource_id)
            resource['__details__'] = stack_resource
        next = resources_to_deploy_next(resource_map, stack_name)
        if not next:
            return
        for resource_id, resource in next.items():
            deploy_resource(resource_id, resource_map, stack_name=stack_name)
    LOG.warning('Unable to resolve all dependencies and deploy all resources ' +
        'after %s iterations. Remaining (%s): %s' % (iters, len(next), next))
def is_deployable_resource(resource):