Add support for mdn DOM docs

[theinterned]

This is a great Workflow! I'd just love to see DOM docs in there.

I tried to add in DOM docs by copying the js docs example and updating the type to "dom" and the $data source to http://dochub.io/data/dom-mdn.json

The results display properly, but the enter key doesn't load the docs in my browser.

Anyways, this seems like a simple enough update - I can make a pull request with my slightly broken attempt.