Implicit `summary` and `description`

Hi!

There’s one thing in _jsDoc_ that I really liked. The two examples were implicitly equivalent:

``` js
/**
* A one-line description of the function’s purpose
*
* A nice multiline description here. Blabla bla bla blablabla. More docs.
* Just static text.
*/

/**
* @summary A one-line description of the function’s purpose
* @description
* A nice multiline description here. Blabla bla bla blablabla. More docs.
* Just static text.
*/
```

The first one is obviously more readable!

How about mapping this to _rfx_? How about (for example) making these two equivalent?

``` js
rfx({doc: `
A one-line description of the function’s purpose

A nice multiline description here. Blabla bla bla blablabla. More docs.
Since we're in ES6, it supports injected ${ vars }.
`});

rfx({
summary: 'A one-line description of the function’s purpose'
description: `
A nice multiline description here. Blabla bla bla blablabla. More docs.
Since we're in ES6, it supports injected ${ vars }.
`,
});
```

Start by locating the rfx handling for the doc, summary, and description options; the issue names no files or tests. Compare the two JavaScript forms shown and define completion as making the implicit doc form equivalent to the explicit summary and description form, including interpolated template content.

Written by the indexing model from the issue text.