Add benchmark script

* Structure `cli` crate as both a library and an executable, so that
benchmarks can import code from the crate.
* Import macros in the Rust 2018 style.

cli/src/logger.rs

@@ -23,7 +23,7 @@ impl Log for Logger {
     fn flush(&self) {}
 }
 
-pub(crate) fn init() {
+pub fn init() {
     log::set_boxed_logger(Box::new(Logger { filter: None })).unwrap();
     log::set_max_level(LevelFilter::Info);
 }