Added function Top 500

Myself, I never have an idea what to listen to, so I just let grooveshark play the TOP 500 of that day. Now, when I am running I can't really access grooveshark so I needed an off-line library.

Your tool was great except for the fact that it could only download one song at a time or after searching all songs individually I would get my list. So I implemented a function that would automaticly download the full top 500.