PIMD Preview Plugin

```html +preview
<p>Example</p>
```

npm i pimd @pimd/preview-plugin

···
const { Document } = require("pimd")
const Config = require("pimd/lib/config")
const previewPlugin = require("@pimd/preview-plugin")

const config = new Config()
config.use(previewPlugin)

const markdown = `
···
\`\`\`html +preview
<p>Example</p>
\`\`\`
`
const doc = new Document(markdown, config)
console.log(doc.render())