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/lib.rs

@@ -0,0 +1,10 @@
+pub mod error;
+pub mod generate;
+pub mod loader;
+pub mod logger;
+pub mod parse;
+pub mod test;
+pub mod util;
+
+#[cfg(test)]
+mod tests;