level-search

hi,

I just noticed this module yesterday,
which was exciting, because I had just implemented a
search api for `level`.

basically, each pair of keys in every document are indexed:

``` js
{ name: 'foo',
repository: { type: 'git', url: 'https://github.com/foofoo/foo.git'},
dependencies: {
bar: '1.0.0'
}
}
```

would index that file by the pairs:

```
name foo
repository type
repository url
type git
url https://github.com/dominictarr/level-search
dependencies bar
bar 1.0.0
```

this makes it possible to do nearly any search,
you could probably get really clever, but as a first step,
I just search on the pair that seems the least likely,
and then filter.

is there a way to get the keys involved in the query from jsonquery so that I could combine it with level-search?