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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import re
import json
import yaml
import logging
import traceback
from six import iteritems
from six import string_types
from localstack.utils import common
from localstack.utils.aws import aws_stack
ACTION_CREATE = 'create'
PLACEHOLDER_RESOURCE_NAME = '__resource_name__'
LOG = logging.getLogger(__name__)
UPDATEABLE_RESOURCES = ['Lambda::Function', 'ApiGateway::Method']
def str_or_none(o):
    return o if o is None else json.dumps(o) if isinstance(o, (dict, list)) else str(o)
def select_attributes(obj, attrs):
    result = {}
    for attr in attrs:
        if obj.get(attr) is not None:
            result[attr] = str_or_none(obj.get(attr))
    return result
def get_bucket_location_config(**kwargs):