refactor directory structure and modularize a few common functions

lib/cli.js

@@ -0,0 +1,9 @@
+#!/usr/bin/env node
+
+import { spawn } from "child_process";
+import hugo from "../index.js";
+
+const args = process.argv.slice(2);
+
+spawn(hugo, args, { stdio: "inherit" })
+  .on("exit", process.exit);