Constructs a range using the given begin and end. If the exclude_end parameter
is omitted or is false, the rng will include the end object; otherwise, it will be excluded.
static VALUE
range_initialize(int argc, VALUE *argv, VALUE range)
{
VALUE beg, end, flags;
rb_scan_args(argc, argv, "21", &beg, &end, &flags);
range_modify(range);
range_init(range, beg, end, RBOOL(RTEST(flags)));
return Qnil;
}