[racket] New web pages!

Racket now has a new look for its web presence. You can see it at
http://racket-lang.org (modulo DNS propagation).

The new pages improve on the old in several ways:

 * More information is now on the front page.
 * The site works much better small devices, such as phones.
 * It's easier to find important parts of the site, like the package directory.
 * The download process is more streamlined -- now it's only 2 clicks.

We also wanted to have a new look, and a description that talks about
why Racket is exciting.

Finally, we've taken this opportunity to shift our web hosting
entirely to Amazon S3, for which Greg Hendershott's `aws` package [1]
has been very helpful.

While the new pages have been under development for quite a while,
we're still happy to take bug reports, suggestions and (especially)
patches: all of the site can be found here:
    https://github.com/plt/racket/tree/master/pkgs/plt-services/meta/new-web
with the framework for building the site here:
    https://github.com/plt/racket/tree/master/pkgs/plt-web-pkgs

The site is built using Eli's `scribble/html` library [2], which is
very nice to use.

I'd especially like to thank Eli and Matthew for their help with this
-- going from my hacked-up HTML prototype to the smooth-building and
well-organized code we have now has taken lots of work.

Sam

[1] https://github.com/greghendershott/aws
[2] http://www.cs.utah.edu/plt/snapshots/current/doc/scribble-pp/html.html