Should matched selectors be returned alongside declarations?

This may not be useful in simple string matching like `'.foo'` but what about for regex matches?

For example, here is functionality as of v0.3.0:

_./stylesheet.css_
```css
.foo {
color: blue;
}

.footer {
color: black;
}
```

```javascript
declarations = styledImport('./stylesheet.css', /foo/)
// declarations is 'color: blue;'

declarations = styledImport('./stylesheet.css', /foo/g)
// declarations is ['color: blue;', 'color: black;']
```

Would it be better to return the selectors also? For example:

```javascript
matches = styledImport('./stylesheet.css', /foo/g)

// matches could be:

[{
selector: '.foo',
declarations: 'color: blue;'
}, {
selector: '.footer',
declarations: 'color: black;'
}]
```

There are probably other cases where having selectors back would be useful.

It could be behind an options flag of some sort.

The issue names no source files or tests; start by locating the styledImport entry point and its regex-matching behavior using the stylesheet.css examples. Review how simple and global matches currently differ, then determine whether selector/declaration pairs and an options flag fit the API. Done means the behavior and compatibility choice are clearly specified and covered by tests.

Written by the indexing model from the issue text.