Errors and document for beginners:
----------------------------------

E D
* * dir-lib.ss          
* * docs-lib.ss         
* * elevator-lib.ss
* + hangman-lib.ss 
* - master-lib.ss       
* + draw-lib.ss
* + rectangle-lib.ss    
* * pingp-play-lib.ss   
* + pingp-lib.ss        
* * protect-play-lib.ss                     

Factor out functions for testing arguments to libraries: 
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check-proc
