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
Skip deleted comments
Split comments which are longer than Github's limit into multiple comments
Add a note that running this results in emails being sent
Fix for error when running with --dry-run: "UnboundLocalError: local
variable 'github_issue' referenced before assignment"
Encode attachment filename to UTF-8, in case it has non-ASCII chars in
it
Merge pull request #1 from msabramo/misc_fixes_1

Misc fixes 1
Add --skip-closed option
Merge pull request #2 from msabramo/tgoyne_master_skip_closed

Add --skip-closed option
Merge pull request #32 from tgoyne/master

Switch to scraping Google Code