[racket] Rosetta Sokoban Solution

The rather empty page on Sokoban now has a Racket solution.  The creator 
is proud to announce it's the fastest solution (though a couple didn't 
give run times) at ~0.1 seconds.  My thanks to Ryan Culpepper for making 
the binary heap that made this possible.

http://rosettacode.org/wiki/Sokoban#Racket

Also, Racket is one short of Python in popularity.  If someone could do 
two more we'll defeat those lazy Python programmers, probably with less 
work!