Function usage 

pub fn usage() -> String

The choir usage block, as a bare invocation prints it.

Names and one-line summaries only, grouped. The full argument spec of a command is a line of its own and there are thirty-two of them; put them all here and the reader scans a wall of <api> <key-file> for the one word they came for. choir <command> --help prints the spec for one command, which is the question anybody actually has.