Content types
-------------

graceful currently talks only JSON. If you want to support other
content-types then the only way is to override
:meth:`BaseResource.make_body`,
:meth:`BaseResource.require_representation` and optionally
:meth:`BaseResource.on_options` etc. methods. Suggested way would be do
create a class mixin that can be added to every of your resources but ideally
it would be great if someone contributed code that adds reasonable content
negotiation and pluggable content-type serialization.