Support single element or top level arrays

Building on @theianjones's proposal in #3.

> 1 open question is how to represent an array with a single element. The only idea I had was fragments like `<>...`. But that would be a separate PR anyway.

Given a component-like function:

```jsx
const Aliases = () => (
<>



)
```

Expect ``:

```json5
[
{
// name: "alias",?
from: "react",
to: "preact-compat",
},
{
// name: "alias",?
from: "react-dom",
to: "preact-compat",
},
]
```

Given:

```jsx
const Resolve = () => (

<>



)
```

Expect ``:

```json5
{
name: "resolve",
alias: [
{
from: "react-dom",
to: "preact-compat",
},
],
}
```

Start with the proposal referenced in issue #3, then trace how the JSX examples are currently converted into JSON. Verify the two stated cases: a component returning multiple top-level elements becomes an array, while a single element nested in a parent becomes a one-item array. The issue notes that fragment syntax is a separate concern.

Scritto dal modello di indicizzazione a partire dal testo della issue.