boto3 rewrite

[strofimovsky]

Legacy boto broke with the introduction of public snapshots. I patched it, one thing led to another,
it ended up with boto3 rewrite of the script, Lambda compatibility etc: https://github.com/strofimovsky/aws-rolling-snaps

I'd be happy to commit it somewhere (I tried to keep compatibility to the maximum) or you can just link to the new repo. Whatever you think is more appropriate.

Thanks for the great useful tool!