Create Comment model.

Generate a rails model for comments, and migrate the database.
Associate Post model to Comment
Add a Route for Comments
Generate Comments controller
Add Comment form to Posts.show
Wire comments controller create
Display comments on post page.
Merge branch 'comment_model' into develop
Extract comments display to partial.
Extract comments form to partial.
Merge branch 'refactoring' into develop
Add destroy option for comments.
Delete a post's comments when post is deleted.
Merge branch 'delete_comments' into develop
Add HTTP Basic authentication.
Merge branch 'security' into develop
Create tags model and post association.
Implement Tags
Merge branch 'multi-model_form' into develop
Extract tag joining to posts helper.