[racket-dev] Continuous integration for Racket on Windows

Over the last couple days, I've set up a continuous integration system
for Racket that runs on Windows, using the service provided by
AppVeyor. You can see the current state here:

    https://ci.appveyor.com/project/plt/racket

It's configured by the `appveyor.yml` file in the root of the
`plt/racket` repository. It builds Racket on every push.

Currently, it only runs the tests for the core, and unfortunately it
times out before finishing those, so all the builds are failures.
Hopefully we'll be able to reduce the time needed for this so that it
can complete -- I have some ideas.

Right now, it only sends notifications to me on failed builds, but if
you break the build or tests on Windows I'll probably send you an
email.

Happy hacking,
Sam