Hole type: subroutine
Write a subroutine which, given a string consisting entirely of
hexadecimal digits, converts pairs of digits to their ASCII character
equivalents and returns the result as a list of characters. The
hexadecimal digits A-F may appear in upper or lower case. There will be
an even number of digits in the string.
e.g.
5065726c206861636b6572
->
('P', 'e', 'r', 'l', ' ', 'h', 'a', 'c', 'k', 'e', 'r')