420 change to 4chan

mootykins changed some URLs, and the HTML.  At least he announced the API changes before they happened.  I'm guessing the 4chan API will change less often & more slowly than the HTML.

An update to notifier.py is getting sucked up in this pull request.  I'd feel better if I did more testing to that thing.  (looks closer) looks like I don't have a test suite at ALL for that.  I'll get on that tomorrow and make another pull request specifically for that.  I remember I wanted to improve detecting RSS updates, maybe more methos than just HTTP HEAD since we know we can't rely on that in every case.