[syntax] :char-range vars min max

SRFI-42: Runs through a range of characters. First min and max are evaluated, which must result in two characters a and b. Then the sequence of characters a, a+1, a+2, ..., b is enumerated in the order defined by char<=? in the sense of [ R5RS 6.3.4.]. If b is smaller than a then the sequence is empty. (Note that b is included in the sequence.)