Infrequent Access storage class

[AMeng]

I'd like to add the ability to use the Infrequent Access S3 storage class for backups. This requires upgrading to boto3. Would that be an acceptable change?

[JeremyGrosser]

I'm generally in favor of switching to boto3, but I was hoping to get some better test infrastructure setup before making any major changes to tablesnap... I don't currently run a production Cassandra environment, so it's a bit labor intensive to validate that everything's working as intended right now.