[racket] recent updates to Whalesong development: web-world

We're smack in the middle of implementing web-world for Whalesong,
which is analogous to regular world, but with web pages.  Unlike
regular world, the callbacks in web-world take in both the world as
well as a functional representation of the DOM.


We have a few programs and some initial documentation on this.  The
documentation for the web-world API is:

    http://hashcollision.org/whalesong/#(part._.The_web-world_.A.P.I)


Here are two toy examples.  (Note: try the examples in Chrome.
Firefox will almost certainly not work.  See:
https://bugzilla.mozilla.org/show_bug.cgi?id=676343 for details.)

    http://hashcollision.org/whalesong/examples/todo/todo.xhtml
    https://github.com/dyoo/whalesong/tree/master/web-world/examples/todo

    http://hashcollision.org/whalesong/examples/attr-animation/attr-animation.xhtml
    https://github.com/dyoo/whalesong/tree/master/web-world/examples/attr-animation


I'd like some feedback on the API; does this seem like a convenient
model for writing web programs, or is it missing something crucial?