Support for "none python" parameters used in the put_object method

There are parameters available in the Facebook API that can not be represented by python arguments, for instance "fb:explicitly_shared" (https://developers.facebook.com/docs/opengraph/guides/explicit-sharing/). Therefore there is a need to make the put_object method more flexible. I suggest doing so by allowing a post_args dictionary as a method argument. Since there might be conflicts between the post_args dictionary and the kwargs, I've implemented it in such a way that the kwarg always will take precedence.