[racket] tutorial: exploring the boundaries of outer space

I'll be releasing an update to my "outer" tutorial shortly, but would
like to double check that the result I'm aiming toward is of good
quality before I finish the text.


I've ended up with:

    https://github.com/dyoo/outer-tutorial/blob/master/outer.rkt

which takes components of Eli's solution, plus a little extra work to
let "outer" act as a hygienic macro.  Tests in:

    https://github.com/dyoo/outer-tutorial/blob/master/test-outer.rkt
    https://github.com/dyoo/outer-tutorial/blob/master/test-outer-renamed.rkt

appear to be doing something reasonable.


Please let me know if I've missed something crucial.  Thanks!