[racket-dev] Racket Guide chapter on concurrency

Hi all,

At the hackathon Asumu helped me work on a Guide chapter on concurrency.

Thanks Asumu!

Since then I've fleshed it out some more and pushed a commit to github.

https://github.com/davidtpierson/racket/commit/d2fb857efec8ce508ac6f76afa845d788edab4c1

It probably needs more work.  I would love some feedback before I dare to
submit a pull request.

Some of my concerns, in no particular order:

1) Should it be broken into separate pages?

2) It starts out with the basics of threads.  Is this too trivial to cover?

3) There are lots of ways to synchronize Racket threads.  I try to cover them
broadly, but don't really delve into which ones are best.  Parts seem like
they are just restating information from the reference.  Should there be more
prescriptive text?

4) Some of the examples feel clumsy.  Contriving concurrency examples
that are both simple and meaningful was hard.  I'm not sure I succeeded.

Thanks for any feedback (on the above issues or anything else.)

David