Changed the fields fn into an accessor property.
This feels more pythonic to me....
Implemented collection as an iterator.
Now instead of using a function get_all() to traverse the collections
object, you can simply use a for loop. Also handles when there are more
objects than will be presented in a single page -- iteraters using the
meta "next" url. Also, added a .meta to the collection for the current
metadata from tastypie.