Initial bug migration

[Sam Tobin-Hochstadt]

Summary: if you get a lot of email from github about bugs, do not be alarmed.

I've started migrating bugs from our installation of Gnats to GitHub.
I've begun with Typed Racket bugs, because I know those best, and
because the TR developers are already using Github bugs.

You can see what the migrated bugs look like here:
https://github.com/racket/typed-racket/issues?q=label%3Agnats-migrated

The migrated bugs will be closed automatically soon.

If you haven't previously, go here: http://huor.soic.indiana.edu:8080/
to authorize me to post bugs and comments as you as part of the
migration.

Gnats is still working, and will be for a while. The next step will be
finishing the Typed Racket bug migration, and enabling (optionally)
submitting bugs to GitHub from inside DrRacket. Once that's done, I'll
move to other components of Racket.

Let me know if you have any questions about this, or you have feedback
about the process, or anything else.

Sam, bug czar