docs: add example scheme programs

examples/maps.scm

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+; Higher-order list operations.
+(display "squares: ")
+(display (map (lambda (x) (* x x)) '(1 2 3 4 5)))
+(newline)
+
+(display "odds: ")
+(display (filter odd? '(1 2 3 4 5 6 7 8)))
+(newline)
+
+(display "sum via fold: ")
+(display (fold-left + 0 '(1 2 3 4 5 6 7 8 9 10)))
+(newline)
+
+(display "zip-add: ")
+(display (map + '(1 2 3) '(10 20 30)))
+(newline)
+
+(display "for-each: ")
+(for-each display '(a b c d))
+(newline)
+
+(display "append+reverse: ")
+(display (reverse (append '(1 2) '(3 4) '(5 6))))
+(newline)