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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for resource_id, resource in iteritems(resources):
        if is_deployable_resource(resource):
            if not is_deployed(resource_id, all_resources, stack_name):
                return False
    return True
def resources_to_deploy_next(resources, stack_name):
    result = {}
    for resource_id, resource in iteritems(resources):
        if should_be_deployed(resource_id, resources, stack_name):
            result[resource_id] = resource
    return result
def get_resource_dependencies(resource_id, resource, resources):
    result = {}
    dumped = json.dumps(common.json_safe(resource))
    for other_id, other in iteritems(resources):
        if resource != other:
            
            search1 = '{"Ref": "%s"}' % other_id
            search2 = '{"Fn::GetAtt": ["%s", ' % other_id
            if search1 in dumped or search2 in dumped:
                result[other_id] = other
            if other_id in resource.get('DependsOn', []):
                result[other_id] = other
    return result