Define upper-lower case conversion.
define_case (Integer_Type ch_up, Integer_Type ch_low);
This function defines an upper and lowercase relationship between two
characters specified by the arguments. This relationship is used by
routines which perform uppercase and lowercase conversions.
The first integer ch_up is the ascii value of the uppercase character
and the second parameter ch_low is the ascii value of its
lowercase counterpart.
strlow, strup