Re-run these with the official rust runtime

[euank]

Here's the things I'd like to see for a re-run. I think, given there's a new option worth exploring, it'll be reasonable to re-do these soon and write a followup post about results again.

• Add a trivial example for https://github.com/awslabs/aws-lambda-rust-runtime
• Update setup to not wait ages between 'cold' runs
• Add a fleshed out example for each runtime (e.g. unmarshal json payload of size X, make s3+dynamodb request to do Y, return json response of Z type thing).
• Use different release options (per Consider using different release options for rust projects #2)