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
add clause-name to define-metafunction, to be used with the
newly extended metafunction-cases
Synch German string constants with latest.
add a test for drdr's consumption to keep the ryr models in sync
Turn off DrDr testing
check errors earlier in judgment-form

closes PR 13609
closes PR 13610
adjust docs for check-metafunction to make the example
use more representative

closes PR 13614
document define-metafunction's contract patterns properly

closes PR 13613
adjust commit 99ff0adbfda87791a99914b69caa0decef79cd04 to
be more friendly to the test suites
make check-metafunction and check-reduction-relation
pay attention to the contract/#:domain spec

closes PR 13616
Fix parsing of dotted formals.

Closes PR 13576.
windows: extflonum support

Enable extflonums in a MSVC build by relying on a MinGW-built DLL,
"longdouble.dll". The DLL is loaded on startup. If the DLL isn't
available, then `extflonum-available?' reports #f.

Instead of setting the floating-point mode globally to extended
precision, the mode is changed only just before (and restored right
after) extflonum arithmetic operations.
add a #:pre keyword to define-metafunction

The keyword allows the specification of contracts
that relate different arguments

closes PR 13617
fix header-file issues
avoid compiler warnings
fix non-extflonum build
more fixes to avoid warnings