Feature/bookmark count

Rather than looking for regex `\d*` and replacing it, I think it would be a lot more robust and maintainable/extendable to wrap the number in a span that can be targetted for replacing text. Probably targetted with a `data-` attribute, since that's recommended for JS targetting. 

How about a `(<span data-replaceable-text='bookmarks'>XXX</span>)`, and then the JS can do more like

    $('#bookmarks_nav span[data-replaceable-text=bookmarks]').text(  response.bookmarks.count );

Among other things, this lets people customize the way it looks (say, they prefer not to have parens), and the JS is fine with that, the JS just replaces the entire content of the span wherever it is, and the custom HTML can put it wherever it wants.