Add CloudFormation utility functions

This adds some general-purpose functions to create or update an AWS CloudFormation stack from a JSON template file.
Oh, OK. I wasn't aware of that Python convention. This is a total typography-level-obsessive-compulsive-thing here, but I like single quotes when I can use them because they're less visually noisy. But I can change that to conform to Python conventions, because if there's that convention then single-quotes are actually _more_ noisy to Python people.