Added the ArticleController code and spec for the #create action.

Note that this is the only method (so far) that has to be explicitly implemented because InheritedResources::Base apparently *does not* just Do The Right Thing. "Why?" is a very good question; at first I attempted the workaround documented in https://github.com/josevalim/inherited_resources/issues/9, but was unable to get it working. (Perhaps it only works for the 'success' cases?)

Also minor formatting cleanup in spec.