S9 LIB  (string-upcase string)    ==>  string
        (string-downcase string)  ==>  string

        (load-from-library "string-case.scm")

Return a fresh string containing the characters of STRING, but
with the case of alphabetic characters converted. STRING-UPCASE
converts characters to upper case, STRING-DOWNCASE to lower case.

(string-upcase "Hello, World!")    ==>  "HELLO, WORLD!"
(string-downcase "Hello, World!")  ==>  "hello, world!"
