Allowed for posting of articles

A visitor to the site can add an article with a required title field and a URL and/or content field. Currently very basic (read: ugly) and can allow the posting of an "article" with only a title and no URL or content.

Once I get the functionality set, I'll add some visual improvements. I've also decided to keep the controller specs that Zachary helped me with (for the immediate future, at least).
eventually you may want to move this into `views/layouts/application.html.erb` so that wherever your app ends up redirecting the user, you can be confident that they'll see the flash message.