Rewrite to scrape the site since the API no longer exists

Drops support for handling merged tickets (since the project I'm
importing from doesn't have any, so it'd be an untested mess). Is
probably not backwards-compatible with previously imported issues.

Drops support for Github repos with existing issues since it didn't
actually work.
Add requirements.txt
Update README
Include status updates in migrated comments
Link to the original comment when there's attachments
Fix check for existing comments
Make dates prettier
Also scrape attachments from the initial issue
Add an option to use a cookie for Google Code requests
Link usernames to their Google Code profiles
Use unicode strings where needed