Add wrapper functions to create an "API" for common Hugo commands

[jakejarvis]

Programmatically building a site (especially via webpack, gulp, etc) should ideally be as easy as:

import { build } from "hugo-extended";

await build({
  baseUrl: process.env.DEPLOY_PRIME_URL,
  minify: false,
  enableGitInfo: true,
});

---

This code from the readme would be simplified to something like:

import hugo from "hugo-extended";

// old:
const binPath = await hugo();
execFile(binPath, ["version"], (error, stdout) => {
  console.log(stdout);
});

// new:
console.log(await hugo.version());

---

CLI commands:

• [ ] hugo ➡️ build()
• [ ] hugo start ➡️ startServer()
• [ ] hugo version / hugo env ➡️ version() / version({ verbose: true })
• [ ] hugo config ➡️ getConfig()
• [ ] hugo list [all,drafts,expired] ➡️ getContent() / getContent({ drafts: true} )