output format suitable for importing into couchdb

your module is super useful - huge thanks!

Here's a couple of changes I made so I could import the bookmarks into CouchDB:

- _id is md5 of the url to avoid multiple docs getting written per url
- tags if present are converted into an array so you can do cool things with couchdb views

Feel free to take or leave this, maybe it helps others.

Please be consistent with quote marks

```js
var tags = bookmark.tags === undefined ? [] : bookmark.tags.split(',');
```