Eopl to racket

@dvanhorn - @samth mentioned that you maintained the eopl lang. 

Migration of the EOPL lang to use racket as opposed to mzscheme. 

All mzlib and mzscheme bindings removed. 

Provided lang forms removed: 
transcript-on transcript-off

Notable changes: eopl.scribl
*3-columns is rewritten and tolerates when the number of forms reprovided isn't evenly divisible by 3. 

private/sllgen.rkt
-define-syntax-set removed in favor of begin-for-syntax and define-syntax

Tests pass.