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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region_name = extract_region_from_arn(queue_arn)
    queue_name = sqs_queue_name(queue_arn)
    client = connect_to_service('sqs', region_name=region_name)
    response = client.get_queue_url(QueueName=queue_name)
    return response['QueueUrl']
def sqs_receive_message(queue_arn):
    region_name = extract_region_from_arn(queue_arn)
    client = connect_to_service('sqs', region_name=region_name)
    queue_url = get_sqs_queue_url(queue_arn)
    response = client.receive_message(QueueUrl=queue_url)
    return response
def mock_aws_request_headers(service='dynamodb', region_name=None):
    ctype = APPLICATION_AMZ_JSON_1_0
    if service == 'kinesis':
        ctype = APPLICATION_AMZ_JSON_1_1
    elif service == 'sqs':
        ctype = APPLICATION_X_WWW_FORM_URLENCODED
    access_key = get_boto3_credentials().access_key
    region_name = region_name or get_region()
    headers = {
        'Content-Type': ctype,
        'Accept-Encoding': 'identity',
        'X-Amz-Date': '20160623T103251Z',
        'Authorization': ('AWS4-HMAC-SHA256 ' +
            'Credential=%s/20160623/%s/%s/aws4_request, ' +
            'SignedHeaders=content-type;host;x-amz-date;x-amz-target, Signature=1234') % (
                access_key, region_name, service)
    }
    return headers
def dynamodb_get_item_raw(request):