Function checkpoint_path 

pub fn checkpoint_path(state_dir: &Path, stream: &str, subject: &str) -> PathBuf

Path of the checkpoint file for one stream and subject.

Examples

checkpoint_path("/state", "labjack", "avenars.i69.mu1.lj2.live.ch08")
    -> "/state/labjack/avenars.i69.mu1.lj2.live.ch08.json"