Refactor build_comment() so we don't waste time getting titles for videos that won't be listed due to the character limit

Instead of getting all video titles then formatting the links and appending to the comment body, format links and append them immediately after getting the video title. This way we can cut out as soon as the comment hits the character limit. This should also eliminate the need for the trim_comment() function, since we'll stop building comments before they hit the limit.