Readline-to-Racket: Use racket everywhere.

Readline-to-Racket: Rename file to mzrl.rkt to rktrl.rkt
Games:Remove-mzlib-unitsig-and-cleanup
-Remove all instances of mzlib/unitsig in favor of racket/unit
-Prefer /infer forms.
-move to #lang racket from (module ... racket forms
in the modified games and files.
-remove some lingering scheme imports.
-update documentation

-Paint-by-Numbers:
-move to racket/unit
-update solution and problem gen files to generate using racket/unit
-regen the problem and solution sets using racket/unit
Browser-to-Racket
Update the browser collection to use Racket lang instead of mzscheme.
Move algol-60 collection from mzscheme to racket lang.
-remove mzlib and mzscheme imports
-Small cleanups.
-Ensure tests pass.
-Small indentation fixes