Some updates

1. Remove one line `subps = BeautifulSoup(subps_html)`, it is repeated.
2. Adjust some code to PEP8 format
3. Add a method, `_add_head` and only python code has the `coding=utf-8` line
4. Removed the Django dependence, retrieve question names only by question URL links (django may overkill for this tool)
5. (A few places) Using BS4's CSS selection method to retrieve HTMLs instead of find_all
6. Add a method, `_limit_line_length` to limit the length of comments (for python only)