add support for (static) JS input

It would be cool to be able to pipe JS expressions into `util-inspect`:

```shell
echo '{foo: [{bar: 'baz'}]}' | util-inspect --js
# { foo: [ { bar: 'baz' } ] }
```

It shouldn't *evaluate* the JS expression though, as e.g. `curl | util-inspect` might easily get abused then, but it could

1. parse the JS using [acorn](https://github.com/acornjs/acorn)
2. check if its static (only `ArrayExpression`, `ObjectExpression`, `Property`, `Identifier`, `Literal`)
3. evaluate it
4. inspect it as with JSON input