[Feature request] Allow deploy only if changed.

[vidia]

I am working with versioning my lambda functions and I am realizing two things.

1. I cannot verify that the code I have locally has been deployed (either "deployed to any alias" or "deployed to X alias")
2. I have to deploy the same code again to confirm it is deployed. This means my version numbers are climbing really fast.

Obviously version numbers don't matter, but if lambda is charging me for storage (though the cost is miniscule, a fraction of a fraction of a cent) I think it would be awesome to check for changes before deploying with this tool.

Maybe keep track of the version and alias for a given deploy and then when redeploying to that alias, check that the code is the same as the previously pushed version as well as that the alias is assigned to that version.