Symbol.for("observablehq.display")

[Fil]

closes #51

To use:

```js
display(
  Object.assign([...penguins], {
    [Symbol.for("observablehq.display")]: Inputs.table
  })
);
```

TODO:

• Should it also work in ${} interpolations? (This currently applies only in the display function.)
• Test
• Document

Note: it doesn't seem urgent, we could try and see how far we go without this.

[mbostock]

Should we close this for now, and reopen when there’s demand?

[Fil]

yep, it's not high on the list