Ebs-snapper

- Add 'CostCenter' tag feature (51)

- Fix issue with releasing on CircleCI, re-release 0.7.3 as 0.7.4

- Reduce I/O unit reservation for DynamoDB writes, clean up CFN paths (47)

- Fix a permissions issue with invocation of Lambda functions via CloudWatch (41)

- Use a replication alarm threshold more like the snapshot threshold, since it runs just as frequently (40)
- Catch when too many snapshots are in progress and log it, vs. triggering a ticket (40)
- Add CreateSnapshot permission explicitly to the role used by Lambda (40)
- Adjust the CFN resources to be sure the trigger is setup correctly (40)

- Support for cross-region snapshot replication (38)
- Cleanup old versions of EBS Snapper functions during deployment (37)
- Better error logging for bad configurations (28)
- Centralize dummy AWS account number due to moto changes (33)
- Better context objects and documentation (35)