Support for Storage Service Properties (version 2013-08-15)

Support get/set on storage service properties for version 2013-08-15 by adding serialization for new features and fixing the header version at  2013-08-15. Doesn't support any other version of the API for those methods. Not well tested.

This is not ready to be merged but I'm creating this pull request as a way to discuss this feature and to allow people who **really need** cors to use it.

Fixes #128