fix for dissapearing examples tags

The filter_formatter is clearing examples tags. Array.clear ends up clearing the objects in the array, which happens to be the same object that is still available to Examples#tags. Instead we just want to clear out @examples_tags for FilterFormatter.

I'm firing off this PR out before writing a new test. Also, I assume @examples_events should be handled the same way, but I'll come back to this soon if no one beats me to it.