Static website generator
This should be easy. Basically, we need to:

1.  generated assets files (js/css/chunks), it's as easy as `unvue.build()`
2. generated html files based on user-supplied routes:

```js
const unvue = require('unvue')

unvue.generate({
  paths: ['/', '/post/hello', '/post/world']
})
```

The `generate` function might look like:

```js
function generate(paths) {
  const renderer = createRenderer()
  paths.forEach(url => {
    renderer.renderToString({ url }, (err, html) => {
      fs.writeFileSync //...
    })
  })
}
```