Function cargo_from_env 

pub fn cargo_from_env<T: TopLevelCommand>() -> T

Create a FromArgs type from the current process’s env::args.

This special cases usages where argh is being used in an environment where cargo is driving the build. We skip the second env variable.

This function will exit early from the current process if argument parsing was unsuccessful or if information like --help was requested. Error messages will be printed to stderr, and --help output to stdout.