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
avoid printf
fix leading example of 2htdp/planetcute to make it a legal
2htdp/bsl program

closes PR 13844
bring down below 102 columns
Cosmetic restructuring of syntax/modcode.

This work is preparation for exporting more functionality from this module.
Renamed variables for clarity and to eliminate shadowing.
Turned lets into defines.
Split a helper function out from get-module-code in syntax/modcode.

The get-module-path function finds the compiled or source file corresponding
to a module; get-module-code reads and compiles the contents of this file.
Exported two more functions from syntax/modcode.

The get-module-path function was described in the previous commit.
The get-metadata-path function constructs the paths used to saved .zo files
and so forth; e.g. PATH/compiled/NAME_rkt.zo.
Add tests for get-module-path.
Added documentation for get-module-path and get-metadata-path.
Start on some class type rep
Temp commit
More tmp
Tmp fixes to get things to compile
Get Class syntax working at basic level
Add more class type parsing tests
Add a few failure tests
Fix phase of import
Add duplicate checking and tests
Clean up object init and add support for get-field
Make Class type printing a little better

Still needs a lot of improvement, especially pretty
printing with line breaks