Fixes #17: Feature a post

From #17:

One should be able to make a post a "featured post". There should only be one of these. The selection for the featured post shall be on the list of posts page.

If there is a featured post selected, it will be included in a new variable to be rendered, separate from the $miniblog_posts variable. An implementing developer will be able to echo the $featured_post into some place as desired, and it will follow the defined post template.

@gholtslander @jrans-va

I have included sample usage in the `index.php` file as well, showing that it will only appear if there is a featured post, and if they are not viewing a single post. In some cases, some people may want their featured post shown all the time, regardless of where they're looking (Dad, I think this would be appropriate in the case of the turfit site).
Making sure to add the new database info to the install script, apparently that's pretty vital to the process :boar: