Transition CLI interface to compile-time construction

[alilleybrinker]

clap, which we use to define our CLI interface, has two mechanisms you can use for that definition. Currently, we use the runtime mechanism, but it would be better if we used the compile time mechanism. You trade-off a bit for a slower compile time to do the code generation, but you get compile-time validation that the CLI is correct, and it's generally more predictable and less error-prone than the way we do it today.