Novice module can open images from a url

Passing in a URL to novice.open causes problems because of imghdr (it takes a file object or a file system path). 

I'm using urlparse to check whether or not path is a url and, if so, I copy the image to an in-memory buffer for imghdr to read. Using io.imsave seems to default to png regardless of the original file type, so there temporarily will be two copies of the image for now (again, only if path is a url).