Add support for SaveOptions on e.g. create calls

[alimony]

It seems like None is always passed as SaveOptions for object manipulation calls, see for example (it's the first parameter to Create):

https://github.com/ExactTarget/FuelSDK-Python/blob/master/FuelSDK/rest.py#L197

It would be really nice if options could be passed here somehow. In my specific case, I want to change SaveAction to UpdateAdd per:

http://help.exacttarget.com/en/technical_library/web_service_guide/technical_articles/updating_an_existing_subscriber_using_the_create_method_with_updateadd/

But I guess other SaveOptions could be useful too, so a general solution would be better.

I currently solve this by constructing my own SOAP call, which I would rather not, since this SDK is so nice otherwise :)