Rehost images from a variety of places

[joealcorn]

Current plan:

• Each image host subclasses TweetPoster.rehost.ImageHost
• Iterate through subclasses matching a url against a regex
• If match call extract method, which will return an imgur url or None
• Slot the url into the comment

[joealcorn]

Need to compile a list of popular image hosts on twitter really

• [x] Instagram
• [x] yfrog (ew, why do people still use this)
• [x] twitpic.com