Implement Audience Range to follow DTD

[aarti]

Hello, I need to use this on a project and the Audience Range's were not being generated correctly, therefore I added the code for it. I overrode the to_xml method, it is copied from roxml's original to_xml method and then I made minor modifications. All the audience test are now passing and I also added one more. Let me know if something should be adjusted to be included. Thanks Aarti