Some updates

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