[blog] Implement RSS Feeds

- Task: https://www.odoo.com/web?debug#id=9547&view_type=form&model=project.task
- Pad: https://pad.odoo.com/p/r.SIeozbGyEfAhkzKO
Ok, got it! Your `timezone_format = '%a, %d %b %Y %H:%M:%S %z` can return non-ascii characters as it is localized. On my computer (in French) `%b` wil return `déc` for "December". 
Can you make your code more defensive, so that non-ascii characters are properly escaped in your RSS/Atom feed? Or if the RSS/Atom spec always ask for a date in English, we could force the locale for the datetime?