Thread.Thumbs() function to complement Thread.Files()

py-4chan has a function that returns the URLs of all the "files" (practically images only) in a 4chan thread.

I needed a function that would do the same for thumbnails, so I created Thread.Thumbs().

P.S. I created a PyPi package for py-4chan. https://pypi.python.org/pypi/py-4chan/ . If you want to take control over it, make an account there and I'll add you to it.