added docstring to _clean_unrecorded_files
finished method _is_overdue
working on removing overdue image files
changed hot_news_image to hotnews_image
changed hot_news_title_x to hotnews_title_x
copied config.py from bgm_news/config.py
replaced hot_news_title_x with hotnews_title_x
updated code related to hot_news_image
changed hot_news to hotnews
changed remaining hot_news to hotnews
updated _clean_temporary_files
finished _clean_unrecorded_files