Add JSON examples.

So I think I've found a bug because I can't get these new json examples to pass.  For some reason the credit card keeps getting rejected.
This changed as of https://github.com/spree/spree/commit/3a7b70571ed866ac2d95ae3c2ecb2774e5512b2d. `payment_source` needs to be out of the `order` key. Perhaps thats why you cant get credit cards to pass?

I'm reviewing the api guides for 2-3-stable this afternoon. Hopefully that should help to get all the examples here working for 2-3-stable as well.