[racket] For new Racket users

I don't know if it's that useful as a learning tool... but man, it
*is* fun... or was, because level 5 is Python or nothing... 

> > It also looks like there are solutions for lots of languages on a wiki
> > ... but not Racket.

I edited their wiki and added Racket solutions for the first four...

> I'm particularly ashamed of my solution to 2.  Anyway, it was fun, but 
> back to work.

level 2 will always be ugly without the Python maketrans function. I
used a hash: https://gist.github.com/3151724e7ac74264c52e.

I just wish there was something like this but more
language-agnostic... solutions in other languages than Python will
always look clumsy. Besides that, some solutions in the wiki are concise
and nice, but just wrong, so I'm not sure it is that useful for
comparing languages. Probably rosettacode.org or even
pleac.sourceforge.net/ are better... but much boring, of course.

I may still upload something else, though... love puzzles... :P

Joan