Allow extra props for the Widget

Hi, first of all thank you for this flexible library, it worked nicely for my needs and it is well documented.

I found that I need to be able to pass extra props to Ratings.Widget to make it locatable by our browser automated testing (an "id" at least), and also to provide accessibility attributes.

I opened a PR (#6 ) to allow this and I would be grateful if you could check it.

Thanks!