Documentation Updates

Includes redrafted index page and a few new pages:

* [Home](http://suesmith.github.io/openbadges-directory/)
* [Retrieve Badges](http://suesmith.github.io/openbadges-directory/directory-api)
* [Search for Badges](http://suesmith.github.io/openbadges-directory/search-for-badges)
* [Get Recent Badges](http://suesmith.github.io/openbadges-directory/get-recent-badges)
* [Find Badge Tags](http://suesmith.github.io/openbadges-directory/find-badge-tags)