Dealing with `get_featured_comment_posts` cache issues:
- Simplified arguments for `get_featured_comment_posts` since we weren't using the additional ones anyway
	- post_id is now the only argument
- Cache key for `get_featured_comment_posts` is post_id
- Cache is cleared on unfeature/feature comment for a given parent post_id
Added delete_featured_comment_posts_cache method.
Fixing some stupid.
Merge pull request #12 from methnen/cache-clearing

Dealing with `get_featured_comment_posts` cache issues: