Adds a basic CloudFiles#container method.

I suspect I'll wind up moving this in the near future to go under a
Containers class contained within CloudFiles. I may break the CloudFiles
features down/group them much the same way that the API doc does.

While the responses, for now, are just parsed JSON, I may later wrap
them in objects somewhat similar to how Fog goes about it to make their
data more readily consumable.  Though I'd like to avoid Fog's two-level
API of "models/collections" vs "requests".

Finally, Client#configure! feels like it should delegate to another
class.  That is, we must have a :user and :api_key at a minimum.  We
should fail fast in the absence of those.  That check could be handled
in another object.  And that object would make it easier to expose
region to the Client.