[racket] PLT Tools webpage

I went to look up the Slideshow webpage today, and noticed that the
tools are pushed into a small section in http://docs.racket-lang.org/.
>From a pure marketing and discoverability standpoint, it would be nice
to have back the top level page linked to from the homepage - at
least, speaking personally, that's how I discovered Slideshow in the
first place, and it gives "standalone" tools like Slideshow and the
webserver some sort of "weight" as more than just racket dialects.

martin