Function delegate 

pub fn delegate<I, S>(bynkc: &Path, args: I) -> ExitCode
where
    I: IntoIterator<Item = S>,
    S: AsRef<OsStr>,

Shell bynkc <args> at bynkc, inheriting stdio, and return its exit code. A spawn failure (a missing or unexecutable binary) is surfaced as a driver error naming the path, so a bad BYNK_BYNKC override is diagnosable.