Zeplin.io does that. We use it at work and though it is a little slow it is certainly a productivity enhancer. But the designs and outcome in the tool are as good as the designer, so consistency is very important.

Sketch + Zeplin are my tools of choice, also! :)

Yeah, I I just checked this tool and was shocked it doesn't export to html/css.... No wonder they give it away for free, but I can't see how this product can succeed.