Report spec

@jackparmer creating a PR to make adding commentary a bit easier!
could we do this without even specifying a `name` here?

I could see a use here, but looking at it, it's not clear where `'my report'` will show up in the document. Also, when you print out a dict, it could very well look like this:

```python
{
    items: [
        { class: 'text', content: '## Subsection', markdown=True },
        { class: 'grid', inline: True, fid: 123, username: 'alex' },
        { class: 'plot', inline: True, fid: 234, username: 'alex' },
        { class: 'text', content: 'Hello, hello', type='caption' },
    ],
    name: 'my report'
}
```

... depending on the hash table that gets built.