Changed the error message in case of a nomination_id not being supplied ...

...in the run method. Some documentation for the most important methods. Moved URL strings to constants at the top of the file.
Yep, I wrote this scraper, and a few others, back when I was at Sunlight. I'm happy to help review, but as I don't currently have any infrastructure depending on the project, I'm leaving it to others to merge things.

I believe you're right about calls to the function error-ing if you drop the `={}` from the call signature -- but I don't think that's a reason not to do it. I suggest getting this one merged, and then doing a PR removing *all* of the `={}`'s in the project, and update any calls to the method that were depending on it.