Commenting

Add commenting feature to Hacker News clone. Also formalizes the relationship between `Articles` and `Users` and includes stylistic changes and some basic refactoring. Resolves #12 .
Since there doesn't seem to be a view setup for this controller, you can probably drop the `helper_method` lines I had above, but I would still recommend structuring this way.  Perhaps you can do something similar in the `ArticlesController`...