Expand description
Top-level clap parser and subcommand enum.
Adding a new subcommand is a mechanical three-edit change: a new
src/commands/<name>.rs module with an Args struct and run()
function, a pub mod <name>; line in src/commands/mod.rs, and a
new variant on Command below. The exhaustive match in main.rs
forces the compiler to refuse to build until the dispatcher is
wired up, which is the structural encoding of R11.