some way to select only elements that have a particular event handler

Split from https://github.com/eeue56/elm-html-test/issues/32 by request.

some way to select only elements that have a particular event handler. In this example, find the `div` with the `onClick` handler, and ignore the other `div`s:

```elm
div []
[ div []
[ div [ onClick MyMsg ]
[ div [] [ text "Click me" ] ]
, div [] []
]
, div [] []
]
```

Possible API:
```elm
Query.find [ tag "div", withHandler "click" ]
```

Start with the nested Elm example and the proposed Query.find [ tag "div", withHandler "click" ] API. Confirm that selection returns only the div carrying onClick and ignores the other divs; the issue does not name implementation files or tests, so those must be located in the repository.

Written by the indexing model from the issue text.