Implement 'char-ci=?', 'char-ci<?', 'char-ci>?', 'char-ci>=?', and 'char-ci<=?'

[Katie Burke]

These should return #t if the relation holds, #f otherwise. They should also be case-insensitive, so the first example should return #t.
http://www.scheme.com/tspl4/objects.html#./objects:s202

(char-ci=? #\W #\w)

Traceback (most recent call last):
File "stdin", line 1, col 2
RunTimeError: unbound variable 'char-ci=?'

(char-ci<? #\a #\B)

Traceback (most recent call last):
File "stdin", line 1, col 2
RunTimeError: unbound variable 'char-ci<?'

(char-ci>? #\a #\B)

Traceback (most recent call last):
File "stdin", line 1, col 2
RunTimeError: unbound variable 'char-ci>?'

(char-ci>=? #\a #\z)

Traceback (most recent call last):
File "stdin", line 1, col 2
RunTimeError: unbound variable 'char-ci>=?'

(char-ci<=? #\a #\z)

Traceback (most recent call last):
File "stdin", line 1, col 2
RunTimeError: unbound variable 'char-ci<=?'